There is an inadvertent inconsistency in the notice for the CPS export
experimental feature as compared to other experimental feature notices.
Change it to be consistent.
Fix a small bug in cmExportPackageInfoGenerator that caused extended
version properties ("compat_version", "version_schema")) to be emitted
when empty. Add a test to ensure this is working as intended.
Fixes: #26264
Add several test cases to verify that install(PACKAGE_INFO) is working
as expected. These cover validating the output for several scenarios,
improper use of the command, effects of command arguments, and a handful
of improper uses.
Tests that should still be added include one covering DESTINATION (both
the default and user-specified) and the CPS location and link_location
attributes. These have been skipped for now because the former requires
actually installing a test project, and the latter involves validating
attributes whose values are platform-dependent. (In particular, I don't
think link_location will appear on not-Windows.) Additionally, there is
no coverage of (other) common install-command arguments such as
PERMISSIONS, COMPONENT, etc.; however, because the logic implementing
these is shared, the tests covering them for other sub-commands is
probably sufficient.
Note that, because the files are generated in a location that includes a
hash of the install destination, and because the default destination is
platform dependent, the tests need to specify a fixed DESTINATION so
that the location of generated files (which we need to inspect and
validate) is predictable.
