Merge topic 'file-set-repr-improvements' into release-3.23

5fa15ec9f3 Help: Document that target_sources defines [INTERFACE_]HEADER_SETS
c5d4812f20 cmTarget: make HEADER_SETS and INTERFACE_HEADER_SETS read-only
05783b168d cmFileSet: store visibility with the fileset

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !7168