Rename the SAML `singleSignOn` nested property to `singleSignOn` so
that we don't get problems when using uppercase environment variable
names.

See gh-20584

Remove the use of `Assert` since it's unavailable that early.

Closes gh-20875

Closes gh-20869

* pr/20832:
  Update copyright year
  Fix WebappLoader constructor deprecations

Closes gh-20832

See gh-20832

See gh-20832

Closes gh-20868

* pr/20847:
  Polish ConditionMessage#because()

Closes gh-20847

See gh-20847

Update `AbstractJarWriter` to ensure that streams are always closed,
even if entries are not written.

Rework the rename logic used to include the reference PDF to try
and workaround the following local build error:

	Encountered duplicate path "reference/pdf/spring-boot-reference.pdf"
	during copy operation configured with DuplicatesStrategy.FAIL

See gh-20829

Relocate `VersionExtractor` to fix a package tangle.

Add tests to ensure that the layer index can support filenames that
contain spaces.

Closes gh-20827

Update the `LayersIndex` class to ensure that layers that do not contain
content are still written.

Closes gh-20858

Update the executable jar appendix to include details of the index
files.

Closes gh-20859

Update the `classpath.idx` format to align with `layers.idx` and allow
third-parties can parse it as YAML

Closes gh-20861

Update the `layers.idx` format so that it is more compact and can be
parsed by third-parties as YAML.

Closes gh-20860

Since the branch name doesn't always correspond to the milestone name,
eg, master.

See gh-20680

Closes gh-20863

Closes gh-20862

This is done by checking for existing issues only in the milestone
corresponding to the current branch. For issues, the milestone is assigned
at the time of issue creation. For PRs, since the branch is different the
milestone can be derived from that while triaging the issue.

Closes gh-20680

This commit adds examples for configuring the default builder to use
an HTTP/HTTPS proxy when building OCI images using the Maven or Gradle
plugin.

Fixes gh-19984

This commit combines index adoc files for single-page HTML and PDF
into one file to remove duplication. It also renames index files to
reflect the separation between source format and generated output
format.

Finishes gh-20829

* pr/20851:
  Change call to createClassLoader(URL) from 'super' to 'this'

Closes gh-20851

ExecutableArchiveLauncher.createClassLoader(Iterator) calls
createClassLoader(URL) method with 'super'. This means overriding
createClassLoader(URL) is not possible without also overriding
createClassLoader(Iterator). The switch to 'this' enables that.

See gh-20851