WIP: Guided Selection

I have attempted to create Guided Selection. So far, I am getting a error despite that the code looks correct.

In addition, I apologize to Halla Rempt. I didn't expect that the author would be halla as I didn't check before commiting and I can't change the author of the commit due to lack of git knowledge (tried searching and no success because of error messages). Maybe the push will have a different user/e-mail address if possible.

Test Plan

1. Load Krita
2. Make a Selection
3. Click on anywhere on the image except the selection.

The test plan above is to verify the algorithm works before proceeding to make the painting selection.

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.