Closes gh-8892

Closes gh-8232

Closes gh-6911

This commit makes sure to honour the `spring.aop.proxy-target-class`
property if set by the user. Previously, the
`PersistenceExceptionTranslationPostProcessor` was always configured to
use cglib, regardless of the value of that property.

Closes gh-8887

Closes gh-8497

Fixes gh-8883

This commit makes sure to honour the `spring.aop.proxy-target-class`
property if set by the user. Previously, the
`MethodValidationPostProcessor` was always configured to use cglib,
regardless of the value of that property.

Closes gh-8869

* pr/8650:
  Polish "Add the ability to disable the trace filter"
  Add the ability to disable the trace filter

Closes gh-8650

See gh-8650

* pr/8813:
  Polish "Fix http status code with unknown log level"
  Fix http status code with unknown log level

Closes gh-8813

This commit changes the http status code to 400 when an unknown log level
is specified.

Closes gh-8798
See gh-8813

See gh-8879

See gh-8879

* pr/8185:
  Polish "Clarify edge case docs on ConditionalOnClass"
  Clarify edge case docs on ConditionalOnClass

Closes gh-8185

Previously, as a result of the changes made in de50cfa2, an
application would fail to start on Google AppEngine as it prevents
the creation of new threads.

This commit updates OnClassCondition so that it falls back to
performing the work on the main thread when its unable to shift it
to a separate thread.

Closes gh-8584

When used as a meta-annotation the value() attribute of
@ConditionalOnClass will fail silently resulting in the @Conditional
nature of the annotation being ignored.

See gh-8185

As `@TestComponent` is an implementation detail at this point really, this
commit removes any reference to it from the doc.

Closes gh-8421

Closes gh-8842

* pr/8683:
  Polish "Add support for HotSwapAgent to devtools"
  Add support for HotSwapAgent to devtools

Closes gh-8683

HotSwapAgent is an open source competition to JRebel. This commit adds
"org.hotswap.agent.HotswapAgent" to the list of known Java agent based
class reloaders. This causes same behavior as when JRebel is used: a full
restart is NOT triggered when any class changes, however LiveReload event
is still triggered.

See gh-8683