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}.

This patch re-assigns the {key Meta arrowkeys} shortcuts that are currently used for `move zoomed area` (which are pretty esoteric, infrequently-used actions), adding {key ctrl} to their shortcuts. This allows us to use their valuable {key Meta arrowkeys} for more useful and commonly-used window management actions:
- {key Meta Left}: quick tile window to the left
- {key Meta Right}: quick tile window to the right
- {key Meta Up}: quick-tile window to the top
- {key Meta Down}: quick-tile the window to the bottom

The patch also sets some default shortctuts for minimize and maximize:
- {key Meta PageDown}: minimize window
- {key 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

- {key meta up} tiles the active window to the top
- {key meta down} tiles the active window to the bottom
- {key meta left} tiles the active window to the left
- {key meta right} tiles the active window to the right
- {key meta PageDown} minimizes the active window
- {key meta PageUp} maximizes and de-maximizes the active window
- {key meta ctrl up} moves the zoomed area up
- {key meta ctrl down} moves the zoomed area down
- {key meta ctrl left} moves the zoomed area to the left
- {key meta ctrl right} 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