Since we schedule frames for each stage view seperately, surfaces receive frame callbacks for each stage view they are visible on.
This is problematic for several reasons. Thus, add a simple heuristic how to choose a primary stage view and only emit frame callbacks when that one updates.
Closes #1325 (closed)
This heuristic is:
- take the fastest stage view where the surface is non-obscured / visible on
- if we have clones, take the fastest stage view the surface or a clone is located on, ignoring obscuredness
- if two stage views run at the same speed, choose one randomly - this could be improved, see !1468 (comment 926160)