Issue a deprecation warning on calls to `cmake_minimum_required` or
`cmake_policy` that set policies based on versions older than 3.5.
Note that the effective policy version includes `...<max>` treatment.
Update the check from commit 5845c218d7 (Deprecate compatibility with
CMake versions older than 2.8.12, 2020-06-12, v3.19.0-rc1~629^2).
Add cmCommand::Disallowed helper to check the setting of a policy that
disallows the command. Add a RunCMake.DisallowedCommands test
placeholder. Add a Help/policy/DISALLOWED_COMMAND.txt file for
inclusion by each policy document to avoid duplication of the common
text.
