Since Hazlecast 3.12, YAML configuration format is supported in
addition to XML. Therefore, this change makes Spring Boot automatically
discover not only `hazelcast.xml` (and `hazelcast-client.xml`), but also
`hazelcast.yaml` (and `hazelcast-client.yaml`).

See gh-16632

This commit reinstates the single-page variant for the Spring Boot
reference documentation.

Now the single and multi-page variants are hosted under the same
`"html"` folder, as `"index.html"` and `"single-index.html"`.
Note that files ending in `"index.html`" are treated as index files by
the spring-doc-resources project and their table of contents do not
display a "Back to index" link.

Fixes gh-16295

See gh-16666

* pr/16666:
  Fix broken link

Closes gh-16666

* pr/16662:
  Fix typo in issue template

* gh-16658:
  Optimize ConfigurationPropertyName.buildToString()

Closes gh-16658

See gh-16658

Closes gh-16649

Closes gh-16629:

Polish contribution to use a factory method in `AbstractJsonMarshalTester`
rather than additional constructor arguments.

Also change the `JsonContent` tests so that the `Configuration` constructor
is package private. This keeps JsonPath classes out of our public API, at
the expense of limiting custom JsonPath configurations to just our code.

See gh-16629

Closes gh-13920

Fix various compiler warnings and apply a little polish.

Update `JacksonTester` so that the JsonPath instance is explicitly configured
with both a `JacksonJsonProvider` and a `JacksonMappingProvider`.

Prior to this commit, the handling of special characters was not symmetrical
between the serialization (handled via the JacksonTester) and the parsing (handled
via JsonPath) due to the fact that JsonPath used `SimpleJson` as its parser.

See gh-16629

Closes gh-16644

* gh-16221:
  Polish "Prevent double update of metrics when CompositeMeterRegistry exists"
  Prevent double update of metrics when CompositeMeterRegistry exists

Closes gh-16221

See gh-16221

See gh-16221

* gh-16474:
  Speed up element equality checks in ConfigurationPropertyName

Closes gh-16474

See gh-16474

Closes gh-16642

Closes gh-16640

Closes gh-16639

* gh-16618:
  Polish "Polish Maven Plugin's tests"
  Polish Maven Plugin's tests

Closes gh-16618

See gh-16618

See gh-16618

Closes gh-16637

Closes gh-16636

Closes gh-16633

* gh-16620:
  Optimize JarEntry construction

Closes gh-16620

This commit avoids calling the underlying ZipEntry.setExtra() method
that is not very inline friendly in cases where there is no extra
information to be set.

See gh-16620

Closes gh-16626