generate_apple_*_selection_file: Improve docs, signatures, error handling

Polish the generate_apple_*_selection_file interface after feedback from 3.29 release candidates:

• Allow callers to capture error messages so they can set their package _FOUND variable to false.
• Allow callers to pass multiple values to list-valued arguments instead of putting the entire list in a single quoted argument.
• Document and test generate_apple_architecture_selection_file support for $(ARCHS_STANDARD).

See individual commit messages for details.

Fixes: #25778 (closed), #25779 (closed), #25780 (closed)
Backport: release