Mixed resolution rendering had some issues with overscan and border
rendering.
- `render_offset` was in display space and not in render space. Is
now replaced by the `overscan_extent`.
- `overscan_extent` introduced that stored the overscan of the render
extent.
- Fixed issues to determine the film sample weight when `scaling_factor`
was used. It didn't match decompose the actual offset making the
length of the same to large, what blurred the final samples.
NOTE: there are some other issues related to border rendering which was
already in main before mixed resolution rendering was added. I assume
that viewport render image in camera view still adds an additional
offset, which should be ignored.
Fixes#119510Fixes#119511
Pull Request: https://projects.blender.org/blender/blender/pulls/119524
8945b29762