Add the following variables:
* Python_EXECUTABLE_DEBUG
* Python_INTERPRETER
* Python_DEBUG_POSTFIX
and target Python::InterpreterDebug.
python_add_library() command Manage DEBUG_POSTFIX target property based
on the value of Python_DEBUG_POSTFIX variable.
Fixes: #25874
Since commit 5537ccd814 (FindPython: Tests optimizations, 2020-10-01)
some FindPython tests fail because the Development component cannot be
found without knowing `CMAKE_LIBRARY_ARCHITECTURE`. Enable at least one
language in each of these test cases to get that value. This is
consistent with use in practice because the Development component does
not make much sense without a language to compile sources anyway.
Fixes: #21277
