There are idf.py hints for helping the user to set component
dependencies properly instead of building sources out-of-component or
including headers from outside the component directory. These are
produced with
tools/idf_py_actions/hint_modules/component_requirements.py.
However, idf.py hints are printed only when the build fails. If the user
starts with a buildable solution then the suggestions to add component
dependencies are not printed.
This commit introduces cmake-level warnings for building source files
from outside the component and including header files without setting up
proper component dependencies.
