Migrate to Python 3.10

This MR lays the ground work for moving Krita to Python 3.10 across all supported platforms. This also implies that a significant cleanup job was undertaken to bring all our patches up to date.

Benefits of this MR:

• updated the PyQt patch for MinGW-- now it will build multi-threaded on Windows too
• fixed the longstanding TODO re: proper detection of the zip bundle

Test Plan

Make a good gallon of coffee, and build Krita across all supported platforms.

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.