Closes gh-21091

Add how-to documentation describing how health information can be
exported to a Micrometer Gauge.

Closes gh-18329

Fixes gh-20665

Closes gh-21082

Closes gh-19782

Fixes gh-21073

Closes gh-20895

Update `JarURLConnection` to ensure that when connections are opened
a new copy of the JarFile is provided.

Prior to this commit, a single `JarFile` instance was shared which meant
that it could be accidental closed if accessed via
`JarURLConnection.getJarFile()`. If the underlying jar file is closed
then it's possible for a `NoClassDefFoundError` to be thrown if running
on JDK 11 with an active `SecurityManager`.

Closes gh-17796

Closes gh-21070

Update `WebMvcAutoConfiguration` to automatically apply cors
configuration to the `WelcomePageHandlerMapping`.

Fixes gh-21048

This commit harmonizes the change made to @DefaultValue to the
annotation processor. If such annotation is added to a scalar value with
no value at all, no default value is produced.

Closes gh-18917

Closes gh-21061

Closes gh-21052

Update `NettyWebServer` so that the `PortInUseException` is not thrown
for permission denied errors.

Fixes gh-19807

Update classes that throw `PortInUseException` so that they also
include the cause. Prior to this commit the cause was not included
which could make diagnosing the real cause difficult.

See gh-19807

Fixes gh-20745

When using constructor binding, if no properties are bound to
a nested property, the top-level instance will be created with a
null value for the nested property.
This commit introduces support for an empty `@DefaultValue` which
indicates that an instance of the nested property must be created
even if nothing is bound to it. It honors any `@DefaultValue`
annotations that the nested property might have in its constructor.

Closes gh-18917

Update `ConditionalOnAvailableEndpoint` so that it now uses the same
matching code as the endpoint filter. This allows the condition to
match endpoint IDs that contain a dash.

In order to share logic, the `ExposeExcludePropertyEndpointFilter` class
has been deprecated and its logic moved to a new `expose` package
under `IncludExcludeEndpointFilter`. This filter is used by both the
`OnAvailableEndpointCondition` and the auto-configuration classes.

Fixes gh-21044

Closes gh-21039

Closes gh-21027

Update the reference documentation with more details about how relaxed
binding works against environment variables.

Closes gh-18215

Closes gh-21025

Closes gh-19972

Fix checkstyle issues from forward merge.

See gh-21022

Closes gh-21022

Update `ExposeExcludePropertyEndpointFilter` so that patterns will
also match endpoint IDs that contain a dash.

Closes gh-20997

This commit makes sure that both the getter and the setter of a
deprecated configuration properties is flagged with `@Deprecated`.

Closes gh-20812

Closes gh-21003

Refine `DataSourceAutoConfiguration` conditions so that an empty
`spring.datasource.url` property can be used to enable the embedded
source.

Fixed gh-20996

Closes gh-20979

Closes gh-20978

Closes gh-20981

Closes gh-20976

* pr/20882:
  Polish "Polish JarFile to extra anonymous inner class"
  Polish JarFile to extra anonymous inner class

Closes gh-20882

See gh-20882

See gh-20882

Closes gh-20963

Closes gh-20623