Add Perspective Ellipse Assistant Tool

This merge request is complete now, needs review to be merged.

The following MR contains code required to add a Perspective Ellipse Assistant Tool in Krita and the project is under SoK'22.

FEATURE: 405643

Test Plan

• Run Krita.
• Select the Assistant Tool Option.
• From the drop down menu in the Tools Option Docker, select Perspective Ellipse.
• Draw a quadrilateral on the canvas, the four corners are adjustable. The quadrilateral has an inscribed ellipse too!

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.