The OLD behaviors of all policies are deprecated, but only by
documentation. Add an explicit deprecation diagnostic for policies
introduced in CMake 3.24 and below to encourage projects to port
away from setting policies to OLD.
The commands moved to shared_internal_commands.cmake
will soon be used directly by FetchContent, which cannot
always include the full ExternalProject.cmake file (e.g. it may
be used in CMake script mode).
Issue: #21703
Add the option to keep the current filestamps when extracting an
archive in ExternalProject_Add.
Enabling this option makes the behavior consistent with how
ExternalProject_Add is used when checking out code from revision
control instead of an archive.
Fixes: #22746
Brad King