Before this change a missing path variable value resulted in a 400
error where in fact the error is due to a mismatch between the
declared @PathVariable and the URI template, i.e. a 500 error.

This change introduced a MissingPathVariableException as a sub-class
of ServletRequestBindingException (the exception previously thrown)
and results in a response status code of 500 by default.

Issue: SPR-13121

Issue: SPR-13128

Issue: SPR-13093

* patch-3:
  Add missing super in test

Closes gh-814

This is a rework of 71783c5d for SPR-12540 for the async extension that
was not merging the internal RequestConfig as it should.

Issue: SPR-13125

Issue: SPR-11807

Issue: SPR-13099

Issue: SPR-13115

Issue: SPR-13129

Ever since @ActiveProfiles was introduced, the declared active profiles
for integration tests have been sorted in order to support unique cache
key generation; however, there are use cases for which the original
ordering should be retained.

For example, Spring Boot's ConfigFileApplicationListener loads
configuration files for active profiles in the order returned by
Environment.getActiveProfiles(), with the assumption that the ordering
matches the order in which the developer declared the active profiles.

This commit maintains the uniqueness of active profiles declared via
@ActiveProfiles but no longer sorts them.

Issue: SPR-12492

Issue: SPR-12991

Issue: SPR-13041

Issue: SPR-13069

In AnnotatedElementUtils, all methods pertaining to merging annotation
attributes have been renamed to "getMerged*()" and "findMerged*()"
accordingly. Existing methods such as getAnnotationAttributes(..) have
been deprecated in favor of the more descriptive "merged" variants.
This aligns the naming conventions in AnnotatedElementUtils with those
already present in AnnotationReadingVisitorUtils.

The use of "annotationType" as a variable name for the fully qualified
class name of an annotation type has been replaced with
"annotationName" in order to improve the readability and intent of the
code base.

In MetaAnnotationUtils.AnnotationDescriptor, getMergedAnnotation() has
been renamed to synthesizeAnnotation(), and the method is now
overridden in UntypedAnnotationDescriptor to always throw an
UnsupportedOperationException in order to avoid potential run-time
ClassCastExceptions.

Issue: SPR-11511

- origin --> origins
- method --> methods
- constants are now actually constant (i.e., static final)

Issue: SPR-11393

Issue: SPR-11393

Issue: SPR-11393

Prior to this commit, there existed several isEmpty() methods scattered
across various utilities such as ObjectUtils, CollectionUtils, and
StringUtils; however, each of these methods requires a cast to the type
supported for that particular variant.

This commit introduces a general-purpose isEmpty(Object) method in
ObjectUtils that transparently supports multiple object types in a
central location without the need for casts or juggling multiple
utility classes.

Issue: SPR-13119

The modifications to DefaultMockMvcBuilder performed in conjunction
with SPR-12553 introduced a breaking change: the WebApplicationContext
supplied to DefaultMockMvcBuilder's constructor was *always* stored in
the ServletContext as the root WebApplicationContext, overwriting a
root WebApplicationContext that had been set by the user or by the
Spring TestContext Framework (TCF) -- for example, in
AbstractGenericWebContextLoader. Consequently, the changes in SPR-12553
cause tests that use @ContextHierarchy to fail if web components rely
on the correct WebApplicationContext being stored under the
WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE key.

This commit reverts the breaking changes introduced in SPR-12553: if
the root WebApplicationContext has already been set in the
ServletContext of the WebApplicationContext supplied to
DefaultMockMvcBuilder, no action is taken.

Furthermore, this commit introduces new code to address the initial
intent of SPR-12553. Specifically, if the root WebApplicationContext
has NOT been set in the ServletContext of the WebApplicationContext
supplied to DefaultMockMvcBuilder, the application context hierarchy
will be traversed in search of the root WebApplicationContext, and the
root WebApplicationContext will then be stored under the
ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE key.

Issue: SPR-13075, SPR-12553

Prior to this change, the `"Last-Modified"` and "`Etag`" support had
been improved with SPR-11324: HTTP response headers are now
automatically added for conditional requests and more.

This commit fixes the format of the "`Last-Modified`" and "`ETag`"
values, which were using an epoch timestamp rather than an HTTP-date
format defined in RFC 7231 section 7.1.1.1.

Also, Conditional responses are only applied when the given response
applies, i.e. when it has an compatible HTTP status (2xx).

Issue: SPR-13090

Issue: SPR-13102

Issue: SPR-13112

Issue: SPR-13108

Issue: SPR-13101

Issue: SPR-13104