Transform Orientation Refactor

- 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

source/blender/editors/transform/transform_constraints.h

@@ -36,7 +36,7 @@ void drawPropCircle(const struct bContext *C, TransInfo *t);
 void startConstraint(TransInfo *t);
 void stopConstraint(TransInfo *t);
 void getConstraintMatrix(TransInfo *t);
-void initSelectConstraint(TransInfo *t, float mtx[3][3]);
+void initSelectConstraint(TransInfo *t, bool force_global);
 void selectConstraint(TransInfo *t);
 void postSelectConstraint(TransInfo *t);
 void setNearestAxis(TransInfo *t);