This patch renames two domains:
- Polygon -> Face
- Corner -> Face Corner
For the change from polygon to face I did a "deep rename", where I updated all (most?) cases where we refer to the attribute domain in code as well.
The change from Corner to Face Corner is only a ui change. I did not see a real need to update all the code for that. I tried it in a few places, but it does not seem to improve the code, more on the contrary.

