Not all the behaviors of CMake variables for ignoring search
locations by find_...() commands were fully documented.
Add the missing effects, clarify the wording and restructure the
way the details are assembled to reduce duplication.
Also improve the cross-referencing to ensure all the related
variables are more discoverable.
Issue: #20878
Run the script:
Utilities/Sphinx/update_versions.py --since v3.22.0 --overwrite
Manually select updates that really belong to the 3.23 release, as
against adding documentation for previously-existing entities.
