Arrow key movement with the Transform tool

This patch adds the ability to move the selection with the arrow keys when using the Transform tool as requested here This uses the keybindings from the Move tool.

This is not pixel perfect: if the width/height of the selection is odd, since the position of the transformation center is rounded to the nearest pixel the selection cannot go back to its original position. This was already the old behavior so I think this is okay but I wanted to document it here.

Test Plan

Select the Transform tool: you can now move the selection around with the arrow keys.

Unit tests: all tests related to the transform tool pass, except for KisAnimatedTransformParametersTest::testTransformKeyframing which also fails on master.

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.