Split from #14293.
It makes sense for a setting that changes visual output to have priority over a setting that barely makes any difference.

Creates a layer outside the game config layer system and passes it to the created gfx widows, so as to not interfere with the global config system.

Supports multiple game properties being open at once.
Supports editing while a game is playing, but the options only save and update the active game when the window is closed.
Right-clicking will remove a property from the game ini.

Adds support for choosing to present the full resolution
independently to each eye when using side-by-side or
top-and-bottom 3D.

Fixes https://bugs.dolphin-emu.org/issues/13593. Before, it would attempt to
use the old shader, which did not exist for the new stereo mode. Changing the
postprocessing shader afterwards would work properly, although passive 3D only
has one option, so it was just broken without restarting Dolphin.

This also fixes the UI not updating when using one of the stereo toggle hotkeys.