Prepare for #140378 by replacing all uses of `ResourceHandle` inside
the engine code with `ResourceHandleRange`.
Aside from the replacement, this changes `ResourceHandleRange` itself
to ensure we use them correctly:
- Prevent direct access to the first handle, to avoid not taking ranges
into account by mistake.
- Add missing functions that are safe to use for ranges
(`has_inverted_handedness` and `is_valid`).
- Add functions that aren't safe to use for ranges, but are required
for the code paths that don't support them yet (these functions assert
that the range points to a single handle, and therefore can be used
safely).
The main change is in `draw_handle.hh`, everything else is just a 1:1
port to use these new functions.
Pull Request: https://projects.blender.org/blender/blender/pulls/140611
7150d0fd1c