FindLATEX: Use FPHSA to report status in standard way

Otherwise LaTeX was marked as not found in the summary.
Also revise the documentation.
find_library: Fix repeat call after changing directory content (#15293)

We use cmGlobalGenerator::GetDirectoryContent to avoid repeating
directory listings.  However, GetDirectoryContent loads content from
disk at most once.  This breaks find_library calls that occur when disk
content has changed since preceding find_library calls.

Teach cmGlobalGenerator::GetDirectoryContent to save the directory
modification time when content is loaded and re-load content if it
changes.

Create a RunCMake.find_library test with a case covering this.
Help: Drop FeatureSummary example in cmake-developer.7

The use of FeatureSummary inside a find module is not a convention
yet used by upstream CMake modules.  Drop the example from the
documentation about how to write find modules.  If in the future
we add use of FeatureSummary to many of the upstream find modules
then this example can be restored as part of establishing the
convention.
Help: Drop FeatureSummary example in cmake-developer.7

The use of FeatureSummary inside a find module is not a convention
yet used by upstream CMake modules.  Drop the example from the
documentation about how to write find modules.  If in the future
we add use of FeatureSummary to many of the upstream find modules
then this example can be restored as part of establishing the
convention.
Merge branch 'backport-doc-find-module-no-summary' into doc-find-module-no-summary

Resolve conflict in Help/manual/cmake-developer.7.rst by taking our
side.
Merge topic 'doc-find-module-no-summary'

3fb33e01 Merge branch 'backport-doc-find-module-no-summary' into doc-find-module-no-summary
d425c110 Help: Drop FeatureSummary example in cmake-developer.7
8235effe Help: Drop FeatureSummary example in cmake-developer.7
Merge topic 'find_library-updated-directory-content'

ce331bab find_library: Fix repeat call after changing directory content (#15293)
Merge topic 'FindLATEX-use-FPHSA'

e0104063 FindLATEX: Use FPHSA to report status in standard way