Add arrow keys to move and resize selection rectangle

Summary:
Add arrow keys to move and resize selection rectangle.
{key Arrows} alone moves in large increment
{key Shift} + {key Arrows} moves in small (single pixel) increments
{key ALT} + {key Arrows} resize rectangle in large increment
{key ALT} + {key Shift} + {key Arrows} resize rectangle in small increment

BUG: 394947

Test Plan:
- Apply patch
 - Launch Spectacle; begin Rectangular Selection
 - Select a rectangle with the mouse
 - Use {key Arrows} to move rectangle (large increment)
 - Use {key Shift} + {key Arrows} to move in small increment
 - Use {key ALT} + {key Arrows} to resize rectangle (large increment
 - Use {key ALT} + {key Shift} + {key Arrows} to resize rectangle in small increment
 - Complete capture with mouse or {key Enter} key
 - Ensure right selection is captured after moving and resizing rectangle

Reviewers: rkflx, ngraham, #spectacle, yurchor

Reviewed By: rkflx, ngraham, #spectacle, yurchor

Subscribers: ltoscano, kde-doc-english, abalaji, #spectacle

Tags: #documentation

Differential Revision: https://phabricator.kde.org/D13450