Merge topic 'post-rel-dev'

1b11f48741 Configure CMake itself with policies through CMake 3.26
ee80960f78 export: Increase maximum policy version in exported files to 3.26
9ba9b6c658 Add deprecation warnings for policies CMP0120 and below

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Merge-request: !8546