Support kwin_blur_v1

[mochaaP]

• Description:
  https://wayland.app/protocols/kde-blur
  Allows us to properly blur regions requested by clients instead of using hacks (e.g. opacity), with possibly increased performance.

[WillPower3309]

Definitely something we can look into! I will mention that quite a few applications don't support this protocol, so we'd want to fall back on opacity (or at least make it configurable)

[mochaaP]

+1 on @WillPower3309, I think a fallback to opacity is required.