Previously, the presence of a src/main/webapp/org directory would
cause the execution of BootWar to fail due to an attempt to write
a duplicate org/ entry to the zip output stream.

This commit updates BootZipCopyAction so that FileTreeElements that
match a directory entry created while writing the loader classes are
skipped.

Closes gh-8972

See gh-8968

Closes gh-8287

Rename WebFluxAnnotationAutoConfiguration to WebFluxAutoConfiguration
to better align with Spring MVC.

Remove the public constant to make it clearer that skipping path
extensions is really an internal Spring Boot concern.

See gh-8765

Replace the MVC validator post processor with an `@Import` so
that a "cannot enhance @Configuration bean definition"
warning does not occur.

Fixes gh-8951
See gh-8495

Closes gh-8961

Closes gh-8960

Closes gh-8959

Closes gh-8958

Closes gh-8957

Closes gh-8956

Closes gh-8955

Closes gh-8954

Closes gh-8953

Windows seems unable to decide if the temp dir is in System32 or
system32 which breaks the comparison. This commit attempts to appease
the gods of case sensitity by reducing the portion of the path that we
check so that system32 vs System32 doesn't come into it.

See gh-8920

Closes gh-8920

Closes gh-8948

Closes gh-8938

Update Spring CLI so that the "resolving dependencies" message is
suppressed when `run --quiet` is used.

Fixes gh-8946

Closes gh-8939

Update `PropertiesLauncher` so that classes can be loaded outside of
`BOOT-INF/classes`. You can use a subdirectory, or the root directory
of an external jar (but not the parent archive to avoid issues
with agents and awkward delegation models).

Fixes gh-8480
Closes gh-8486

Relax `SpringBootTestContextBootstrapper` rules so that a test can
specify an `ApplicationContextInitializer` and still have
`@SpringBootConfiguration` detected.

Prior to this commit detection would not occur because it's possible
that an initializer _could_ register configuration. This scenario is
actually quite unlikely to occur, certainly less likely than wanting to
use an initializer in combination with auto-detection.

Fixes gh-8483

Update `ValidationAutoConfiguration` and `WebMvcAutoConfiguration` to
ensure as much as possible that only a single Validator bean of each
type is registered.

Validation auto-configuration now does the following:
- If no validator is found: Registers a `LocalValidatorFactoryBean`
  (providing both Spring and JSR validation)
- If the user defines a Spring & JSR validator: Backs off
- If the user defines only a JSR validator: Adapts it to a Spring
  validator (without exposing another JSR implementation)

WebMvcAutoConfiguration auto-configuration has been updated to make
MVC validation follow common Spring Boot patterns:
- If not validator beans are found (due to the user excluding
  ValidationAutoConfiguration) a new `mvcValidator` bean will be
  registered.
- If a single validator bean is found it will be used for MVC
  validation.
- If multiple validator beans are defined it will either use the one
  named `mvcValidator` or it will register a new `mvcValidator` bean

Any automatically registered `mvcValidator` bean will not implement
the JSR validator interface.

Finally, it is no longer possible to provide an MVC validator via a
`WebMvcConfigurer`.

Fixes gh-8495

Closes gh-8646