Fix render regions and make them work with overscan:
- Clarify and improve the naming used by the Film module.
- Convert Display texel coordinates to Film texel coordinates before
calling `film_process_data`, and convert from Film texel coordinates to
Render texel coordinates in `film_sample_get`.
- Returns the actual display extent (and not the film extent) in
`Film::display_extent_get` so the overscan camera matrix is computed
correctly when using render regions.
Regression caused by 567a2e5a6f.
Pull Request: https://projects.blender.org/blender/blender/pulls/111691
7e33c405fb