Add a post_package_info hook to check cpp_info.resdirs

[SpaceIm]

see conan-io/conan-center-index#15581 & conan-io/conan-center-index#15599 (comment)

When a recipe is migrated to layout(), cpp_info.resdirs is empty by default instead of ["res"]. For most recipe it's fine and a good default, but few recipes now need to set this attribute explicitly.

I propose this hook:

• Report an error if cpp_info.resdirs miss existing res or share folder in root package folder. Since conan v1 recipes always populate resdirs, this hook shouldn't break them.
• bonus: if a recipe uses layout() (conan v2 recipes only), report an error if cpp_info.resdirs list non-existing folders.