Prior to this commit, dependency injection of all arguments in a test
class constructor invoked by JUnit Jupiter was only possible if the
constructor was explicitly annotated with @Autowired.

This commit introduces support for a configurable "test constructor
autowire" mode which defaults to false in order to remain backwards
compatible.

Specifically, this mode can be configured globally for an entire test
suite via a new "spring.test.constructor.autowire" JVM system property
that can alternatively be configured via the SpringProperties
mechanism. In addition, the global "test constructor autowire" mode can
be overridden locally on a per-class basis via the new @TestConstructor
annotation.

Closes gh-22286

Includes consistent mentioning of ReactiveTransactionManager in javadoc.

Closes gh-22923

DefaultMultipartMessageReader does not cache the part contents, so
binding to the same part multiple times does not work.
Rewrote this test to use separate HTTP request instead.

This commit introduces a way to override the default multipart reader,
for instance to the SynchronossPartHttpMessageReader.

This commit adds proper reference counting to the UndertowDataBuffer.

Normally consumes matches the "Content-Type" header but what should be done if
there is no content? This commit adds checks for method parameters with
@RequestBody(required=false) and if "false" then also match requests with no content.

Closes gh-22010

Includes fix for typo in visitor class names.

See gh-22909

Deprecate the public `StandardMetadata` constructors to make it clearer
that these classes should not be instantiated directly. A new
`AnnotationMetadata.introspect` factory method has been added which
can now be used to obtain instances.

This change will allow use to make the constructors package private
and drop the `nestedAnnotationsAsMap` parameter in a future release.

Closes gh-22906

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

Extract and pull-up some common method implementations and make them
default methods of the interface.

See gh-22884

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

See gh-22884

Update `StandardAnnotationMetadata` to use `ReflectionUtils` when
obtaining declared methods. This update is primarily so that the common
method cache can be used.

Closes gh-22907

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

Add a factory method to `MergedAnnotation` that allows an instance to
be created for an explicit collection of root annotations. This method
will allow ASM based readers to expose a `MergedAnnotation` instance
that has root annotations loaded from bytecode, and meta-annotations
loaded using reflection.

See gh-22884

Update TypeMappedAnnotation so that Strings can be used to represent
Class attribute values. This will allow ASM annotation readers to
present a `MergedAnnotation` instance without necessarily having the
actual class values on the classpath.

When the underlying value is a String, any calls to
`getValue(name, String.class)` or `asMap(Adapt.CLASS_TO_STRING)` will
simply return the original String. Calls that need the actual Class
result (such as `getClass`) will use `Class.forName` and may throw
a `ClassNotFoundException` at that point.

This commit also allows an empty Object[] to be used to represent
any empty primitive array.

See gh-22884

Rename `from` to `of` for the `MergedAnnotation` factory methods that
work with Maps. The previous name was a little confusing, especially
when an annotation source parameter was specified. The new method name
helps to make it clearer when the user is explicitly defining the
attributes of the annotation, as opposed to picking them up from the
source.

Add a `getTypeHierarchy()` method to `MergedAnnotation` that can be used
to return the full type hierarchy information. This method is
specifically designed to be used in combination with
`MergedAnnotationPredicates.unique`.

This update also allows us to delete the `parentAndType` method
from `AnnotatedElementUtils`.

Closes gh-22908

Extract the inner classes from package-info into their own files to
prevent local build problems and to make them easier to find.

Closes gh-22920

Closes gh-22701

We now correctly unwrap suspended resources instead capturing
the Mono emitting suspended resources.

We also properly continue resume by chaining resume Mono's
instead of terminating eagerly.

Closes gh-22893

Closes gh-22701

Closes gh-22912

Closes gh-22903

Merge pull request #22421 from olszewskimichal/LinkedMultiValueMap-OutOfBoundException-When-EmptyList

LinkedMultiValueMap.getFirst - check that values is not empty

This commit introduces the DefaultMultipartMessageReader, a fully
reactive multipart parser that does have any third party dependencies.

Closes gh-21659