Closes gh-23389

Closes gh-23446

* pr/23445:
  Fix multi-release JAR test on JDK 15

Closes gh-23445

Backport of 54f93e9b

See gh-23445

Closes gh-23444

Closes gh-23443

Update `HandlerFunctionDescription` so that it will work with JDK 15.

Closes gh-23442

See gh-23433

See gh-23440

Closes gh-23441

Make `StringSequence.isEmpty()` public for compatibility with JDK 15.

Closes gh-23440

Closes gh-23439

See gh-23433

Closes gh-23433

* pr/21704:
  Polish 'Add origin support for empty YAML list and map'
  Add origin support for empty YAML list and map

Closes gh-21704

See gh-21704

Update `OriginTrackedYamlLoader` to better deal with empty maps
and collections.

See gh-21704

Improve the `JavaBeanBinder` so that an bean that has both a `get` and
`is` method can still be bound.

Closes gh-23007

Update `BootstrapContext` with convenience methods that help if the
type has not been registered.

Closes gh-23438

Change the visibility of our own ConfigDataLocationResolver and
ConfigDataLoader classes so that they can be created outside of
`spring.factories`.

Closes gh-23434

See gh-22983