Closes #22819.

Enforces the following:

• Warns (but doesn't break, for BC) when -m is passed with a .pyf in a -c call, the name is ignored and taken from the .pyf file (the only logical option)
• Each -c run will only produce one python module, so there can only be one .pyf file

There already is a note in the documentation, but this is a much better solution (and also paves the way for #25111).