Introduce opt-out path for xwayland scaling

As kwin works in logical space this means translating from X11 -> Kwin space and then converting back.

The patches come ultimately in two parts:

• In kwayland-server separating client logical space from kwin logical space
• In kwin separating kwin logical space from all X11 calls

Commits have more detail.

If this does land it will be opt-in only.

For testing just run this repo.

Testing instructions

X scale can be set in kwinrc via:

[Xwayland]
Scale=2

Everything will be naturally small.

Run echo Xft.dpi: 192 | xrdb -merge and set various envs as per startplasma-x11 to compensate.

In theory the scale used by kwin for rendering doesn't matter.