Replace the existing ASM based readers with new implementations that
also support MergedAnnotations. The meta-data classes themselves are
now immutable, and constructed via separate reader classes.

The `SimpleMetadataReader` class has been updated to return the new
classes, however the old ones remain since some of them are public
and might be being used directly.

Closes gh-22884

Add `AnnotatedTypeMetaData.getAnnotations()` that can be used to access
annotation details using the `MergedAnnotations` interface.

Where possible, the existing annotation methods have been migrated to
call `getAnnotation()`, rather than needing their own implementation.

The existing ASM based meta-data implementations have not been updated
since they will be deprecated and replaced in a subsequent commit.

See gh-22884

Add some additional tests to provide more coverage of class and method
meta-data support.

See gh-22884

Update `StandardAnnotationMetadata` and `AnnotationMetadataReadingVisitor`
so that `java.lang.annotation` annotations are consistently skipped.

Closes gh-22885

Update ASM based metadata readers so that only RetentionPolicy.RUNTIME
annotations are exposed. This aligned behavior with the reflection based
implementation.

Closes gh-22886

org.junit.Assert.assertThat() is deprecated as of JUnit 4.13.

See gh-22894

Closes gh-22766

This commit updates URLs to prefer the https protocol. Redirects are not followed to avoid accidentally expanding intentionally shortened URLs (i.e. if using a URL shortener).

# Fixed URLs

## Fixed Success
These URLs were switched to an https URL with a 2xx status. While the status was successful, your review is still recommended.

* [ ] http://www.apache.org/licenses/ with 1 occurrences migrated to:
  https://www.apache.org/licenses/ ([https](https://www.apache.org/licenses/) result 200).
* [ ] http://www.apache.org/licenses/LICENSE-2.0 with 6515 occurrences migrated to:
  https://www.apache.org/licenses/LICENSE-2.0 ([https](https://www.apache.org/licenses/LICENSE-2.0) result 200).

This commit updates URLs to prefer the https protocol. Redirects are not followed to avoid accidentally expanding intentionally shortened URLs (i.e. if using a URL shortener).

# Fixed URLs

## Fixed Success
These URLs were switched to an https URL with a 2xx status. While the status was successful, your review is still recommended.

* [ ] http://www.apache.org/licenses/ with 1 occurrences migrated to:
  https://www.apache.org/licenses/ ([https](https://www.apache.org/licenses/) result 200).
* [ ] http://www.apache.org/licenses/LICENSE-2.0 with 6625 occurrences migrated to:
  https://www.apache.org/licenses/LICENSE-2.0 ([https](https://www.apache.org/licenses/LICENSE-2.0) result 200).

Closes gh-2019

See gh-2019

Issue: SPR-17347

Issue: SPR-16667

use assertNull instead of assertEquals(null, value),
declare delta as double value in assertEquals

This commit adds a "spring-context-indexer" module that can be added to
any project in order to generate an index of candidate components defined
in the project.

`CandidateComponentsIndexer` is a standard annotation processor that
looks for source files with target annotations (typically `@Component`)
and references them in a `META-INF/spring.components` generated file.

Each entry in the index is the fully qualified name of a candidate
component and the comma-separated list of stereotypes that apply to that
candidate. A typical example of a stereotype is `@Component`. If a
project has a `com.example.FooService` annotated with `@Component` the
following `META-INF/spring.components` file is generated at compile time:

```
com.example.FooService=org.springframework.stereotype.Component
```

A new `@Indexed` annotation can be added on any annotation to instructs
the scanner to include a source file that contains that annotation. For
instance, `@Component` is meta-annotated with `@Indexed` now and adding
`@Indexed` to more annotation types will transparently improve the index
with additional information. This also works for interaces or parent
classes: adding `@Indexed` on a `Repository` base interface means that
the indexed can be queried for its implementation by using the fully
qualified name of the `Repository` interface.

The indexer also adds any class or interface that has a type-level
annotation from the `javax` package. This includes obviously JPA
(`@Entity` and related) but also CDI (`@Named`, `@ManagedBean`) and
servlet annotations (i.e. `@WebFilter`). These are meant to handle
cases where a component needs to identify candidates and use classpath
scanning currently.

If a `package-info.java` file exists, the package is registered using
a "package-info" stereotype.

Such files can later be reused by the `ApplicationContext` to avoid
using component scan. A global `CandidateComponentsIndex` can be easily
loaded from the current classpath using `CandidateComponentsIndexLoader`.

The core framework uses such infrastructure in two areas: to retrieve
the candidate `@Component`s and to build a default `PersistenceUnitInfo`.
Rather than scanning the classpath and using ASM to identify candidates,
the index is used if present.

As long as the include filters refer to an annotation that is directly
annotated with `@Indexed` or an assignable type that is directly
annotated with `@Indexed`, the index can be used since a dedicated entry
wil be present for that type. If any other unsupported include filter is
specified, we fallback on classpath scanning.

In case the index is incomplete or cannot be used, The
`spring.index.ignore` system property can be set to `true` or,
alternatively, in a "spring.properties" at the root of the classpath.

Issue: SPR-11890

Issue: SPR-14427

Issue: SPR-13188

This commit migrates all remaining tests from JUnit 3 to JUnit 4, with
the exception of Spring's legacy JUnit 3.8 based testing framework that
is still in use in the spring-orm module.

Issue: SPR-13514

This commit picks up where SPR-11483 left off, with the goal of
eliminating all unnecessary inspection of core JDK annotations in
Spring's annotation search algorithms in AnnotatedElementUtils and
AnnotationMetadataReadingVisitor.

Issue: SPR-12989

Issue: SPR-12473
(cherry picked from commit 5ac86803)

ClassMetadata exposes isAnnotation() now, and correctly returns false from hasSuperClass() for interfaces and annotations

Issue: SPR-11711

AnnotationMetadataReadingVisitor passes metaAnnotationMap into getMergedAnnotationAttributes algorithm, for finding out about applicable overrides

Issue: SPR-11649

Prior to this commit, invoking the getMergedAnnotationAttributes()
method in AnnotationReadingVisitorUtils resulted in mutation of the
internal state of the ASM-based annotation metadata supplied to the
method.

This commit fixes this issue by making a copy of the original
AnnotationAttributes for the target annotation before merging attribute
values from the meta-annotation hierarchy.

This commit also introduces a slight performance improvement by
avoiding duplicate processing of the attributes of the target
annotation.

Issue: SPR-11710

Changes introduced in conjunction with issue SPR-11475 altered the
behavior of StandardAnnotationMetadata such that annotations could be
detected on superclasses, specifically in the case where the
AnnotatedElementUtils.getAllAnnotationAttributes() method is invoked to
obtain multiple annotations of the same type (on the lowest level in the
class hierarchy), as is the case for @Profile and @Conditional.

This commit partially reverts these changes as follows:

 - All methods in AnnotatedElementUtils now set the
   traverseClassHierarchy to false, thereby effectively reverting the
   changes made in commit 1d30bf83.
   Note, however, that the changes made to AnnotationUtils remain in
   place.

 - Introduced tests in AnnotationMetadataTests that verify behavior
   present in Spring Framework 4.0.2 and earlier.

 - Updated tests in AnnotatedElementUtilsTests so that they pass against
   the reverted changes (i.e., align with the behavior present in Spring
   Framework 4.0.2 and earlier).

 - Refined Javadoc in AnnotationMetadata with regard to annotations
   being "present" vs. "defined".

 - Refined Javadoc in AnnotatedTypeMetadata.

Issue: SPR-11475, SPR-11595

Prior to this commit, Spring supported meta-annotation attribute
overrides in custom composed annotations with reflection-based
annotation processing but not with ASM-based annotation processing.

This commit ensures that meta-annotation attribute overrides are
supported in AnnotationMetadataReadingVisitor.getAnnotationAttributes().

Issue: SPR-11574

Prior to this commit several test classes named "*Test" were not
recognized as tests by the Gradle build. This is due to the configured
inclusion of '**/*Tests.*' which follows Spring's naming convention for
test classes.

This commit addresses this issue by:

 - Renaming real test classes consistently to "*Tests".
 - Renaming internal test classes to "*TestCase".
 - Renaming @WebTest to @WebTestStereotype.
 - Disabling broken tests in AnnoDrivenStaticEntityMockingControlTest.
 - Modifying the Gradle build configuration so that classes ending in
   either "*Tests" or "*Test" are considered test classes.

Issue: SPR-11384

Fix ASM AnnotationAttributesReadingVisitor to correctly deal with
subclasses enums.

Issue: SPR-10914

Update AnnotationMetadata and MethodMetadata to extend from a new
AnnotatedTypeMetadata base interface containing the methods that are
common to both. Also introduce new getAllAnnotationAttributes methods
providing MultiValueMap access to both annotation and meta-annotation
attributes.

Existing classreading and standard implementations have been
refactored to support the new interface.