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
3fccfe0bc6