This commit expands the migration check to all deprecated properties,
not only the ones that have been effectively removed. This provides more
information upfront, including keys that still work in the current
release but will need to be renamed sooner than later anyway.

Closes gh-21425

See gh-20934

Further improve the performance of `containsDescendantOf` by using
a Map to limit the number of candidates that need checking.

Closes gh-21416

Attempt to improve the performance of the `ConfigurationPropertySource`
adapters `containsDescendantOf` method. The method now operates on
arrays rather than iterators and reduces the inner for-loop when
possible.

See gh-21416

Closes gh-20934

5 seconds isn't always sufficient, particularly on CI where the timing
can be quite variable.

Prior to this commit, if a DOCKER_HOST environment variable was present
when attempting to communicate with a Docker daemon, it was assumed
that the value of that variable was an address that could be used to
create an HTTP connection to a remote daemon. In some cases, the value
of the variable is the path to a local socket file, which would cause
the HTTP connection to fail.

This commit adds additional validation of the value of the DOCKER_HOST
environment variable to determine whether it is a remote address or
a local socket file and create the appropriate connection type.

Fixes gh-21173

Previously, a race between the server starting to reject requests
on a kept-alive connection and the request reaching the blocking
servlet could result in a response never being sent.

This commit updates the test to disable blocking once graceful
shutdown with an in-flight request has being. Awaitility is then used
to make a request on an idle kept-alive connection until it fails
due to the connection reset. This may not happen immediately due to
the aforementioned race.

Closes gh-21429

Closes gh-21375

Closes gh-21347

Closes gh-21325

Closes gh-21391
Co-authored-by: Phillip Webb <pwebb@pivotal.io>

Prior to this commit, details about an exception would get dropped when
the management context was separate from the application context and
an actuator endpoint threw a binding exception.

This commit adds some logic to capture the exception so the management
context error handlers can add the appropriate attributes to the error
response.

Fixes gh-21036

* pr/21390:
  Fix ClientHttpConnectorConfigurationTests.shouldApplyHttpClientMapper()

Closes gh-21390

See gh-21390

Closes gh-21422

Closes gh-21421

Closes gh-21383

Closes gh-21384

See gh-21394

* pr/21394:
  Polish "Calculate hashCode only once in ConfigurationPropertyName"
  Calculate hashCode only once in ConfigurationPropertyName

Closes gh-21394

See gh-21394

See gh-21394

* pr/21417:
  Fix capitalization of Testcontainers in Howto docs

Closes gh-21417

See gh-21417

Closes gh-21418

Closes gh-21415

Closes gh-21414

Closes gh-21413

Closes gh-21412

Closes gh-21411

Closes gh-21410

Closes gh-21409