Expose more default window management shortcuts

Summary:
KWin's window management powers are not as discoverable as they could be--particularly tiling, which by default has no visible UI and no keyboard shortcuts. Resolving this issue is highly relevant to T6831: Top-notch usability and productivity for basic software.

This patch re-assigns the Meta+arrowkeys shortcuts that are currently used for move zoomed area (which are pretty esoteric, infrequently-used actions), adding ctrl to their shortcuts. This allows us to use their valuable Meta+arrowkeys for more useful and commonly-used window management actions:

• Meta+←: quick tile window to the left
• Meta+→: quick tile window to the right
• Meta+↑: quick-tile window to the top
• Meta+↓: quick-tile the window to the bottom

The patch also sets some default shortctuts for minimize and maximize:

• Meta+PageDown: minimize window
• Meta+PageUp: maximize/de-maximize the window

Test Plan:
Do a clean build
make test (no new test failures)
Reboot
Create and log into a new user account

• meta+↑ tiles the active window to the top
• meta+↓ tiles the active window to the bottom
• meta+← tiles the active window to the left
• meta+→ tiles the active window to the right
• meta+PageDown minimizes the active window
• meta+PageUp maximizes and de-maximizes the active window
• meta+ctrl+↑ moves the zoomed area up
• meta+ctrl+↓ moves the zoomed area down
• meta+ctrl+← moves the zoomed area to the left
• meta+ctrl+→ moves the zoomed area to the right

Reviewers: KWin, Plasma, romangg

Reviewed By: KWin, Plasma, romangg

Subscribers: mart, romangg, broulik, jnoack, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D11377