When VSE cache is invalidated (on most VSE edit operation e.g.), or
Blender quits, in some cases (complex and very long edits), the
prefetch job would block several seconds after being requested to stop.
This was because one codepath would keep looping over all frames without
checking for the `stop` flag.
Use `VectorSet`, `Vector` or `Span` instead of `SeqCollection` struct.
It is now possible to use native `for` loops and `SEQ_ITERATOR_FOREACH`
macro can be removed.
Another feature is, sets of strips no longer needs to be freed. However,
this poses a limitation, that query functions can not be used in case,
where these sets need to be available outside of scope where they are
created.
Pull Request: https://projects.blender.org/blender/blender/pulls/111909
The last good commit was 8474716abb.
After this commits from main were pushed to blender-v4.0-release. These are
being reverted.
Commits a4880576dc from to b26f176d1a that happend afterwards were meant for
4.0, and their contents is preserved.
