Blender Git Loki

Fix #35979, #35937, #35739: undo crashes and missing updates with blender
internal viewport rendering. Lots of tweaks here, mainly:

* Stop 3D viewport render and free database before undo.
* Accumulate update flags rather than replace them each time it rerenders, to
avoid previous updates getting lost.
* Don't check against Render struct view parameters for changes, those are set
in the job thread which might not run before the next update call.