For policy-specific tests, use the version before the policy was
introduced. Otherwise, use 3.5 where possible.
Also, remove `cmake_minimum_required()` and `project()` calls from
individual cases where they are handled by `CMakeLists.txt`.
When genex $<TARGET_PROPERTY:...> for properties like INCLUDE_DIRECTORIES
is evaluated as part of add_custom_command or add_custom_target,
genex $<COMPILE_LANGUAGE> and $<COMPLIE_LANG_AND_ID> should be supported.
Fixes: #20926
