Merge topic 'post-rel-dev'

40ade51cc8 Configure CMake itself with policies through CMake 3.21
b3248c083f export: Increase maximum policy version in exported files to 3.21
0f31463c37 Add deprecation warnings for policies CMP0094 and below

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !6615