- Use `t->spacemtx` as the orientation matrix instead `t->orient_matrix`.
- Unify constraint behavior between modal and non-modal.
- Simplify code to remove old workarounds and rearrange struct members.
This fix T66142 since the actual `orient_type` (in the case
`V3D_ORIENT_NORMAL`) is used during Redo instead of always using
`V3D_ORIENT_CUSTOM_MATRIX`).
Differential Revision: https://developer.blender.org/D7469
Follow up of b2ee1770d4c3 and 10c2254d412d, part of T74432.
Now the area and region naming conventions should be less confusing.
Mostly a careful batch rename but had to do few smaller fixes.
Also ran clang-format on affected files.
