Blender Git Loki

Undo System: replace with simpler binary diffing buffer storage

Applying/undoing incremental changes didn't fit well when
mixed with periodic snapshots from mem-file undo.

This moves to a much simpler undo system.

- Uses array storage with de-duplication from `BLI_array_store`.
- Loads the buffer into existing text data,
for better performance on large files.
- Has the advantage that Python operators can be supported
since we don't depend on hard coded undo operations.

Solves T67045, T66695, T65909.