Transform: fix use of "snap_point" property

There is not much documentation on the "snap_point" property, but by
code it is possible to note that it serves to set a target snap point
and is of internal use as it is hidden from the Redo panel.

However, this property was still very dependent on Tools settings and
if set to an operator's call, it changes the scene configurations
inadequately.

Therefore,
- remove this dependency from UI for rotation and resize operators,
- do not change the state of the snap in the scene and
- cleanup the code.

source/blender/editors/transform/transform.c

@@ -1586,7 +1586,7 @@ void saveTransform(bContext *C, TransInfo *t, wmOperator *op)
     /* Update `ToolSettings` for properties that change during modal. */
     if (t->flag & T_MODAL) {
       /* Do we check for parameter? */
-      if (transformModeUseSnap(t)) {
+      if (transformModeUseSnap(t) && !(t->tsnap.status & SNAP_FORCED)) {
         if (!(t->modifiers & MOD_SNAP) != !(t->tsnap.flag & SCE_SNAP)) {
           /* Type is #eSnapFlag, but type must match various snap attributes in #ToolSettings. */
           short *snap_flag_ptr;

source/blender/editors/transform/transform_snap.cc

@@ -147,6 +147,10 @@ bool transformModeUseSnap(const TransInfo *t)
 
 static bool doForceIncrementSnap(const TransInfo *t)
 {
+  if (t->tsnap.status & SNAP_FORCED) {
+    return false;
+  }
+
   return !transformModeUseSnap(t);
 }
 
@@ -525,13 +529,7 @@ void transform_snap_mixed_apply(TransInfo *t, float *vec)
     return;
   }
 
-  if (t->tsnap.status & SNAP_FORCED) {
-    t->tsnap.snap_source_fn(t);
-
-    t->tsnap.snap_mode_apply_fn(t, vec);
-  }
-  else if (((t->tsnap.mode & ~(SCE_SNAP_MODE_INCREMENT | SCE_SNAP_MODE_GRID)) != 0) &&
-           transform_snap_is_active(t)) {
+  if (t->tsnap.mode & ~(SCE_SNAP_MODE_INCREMENT | SCE_SNAP_MODE_GRID)) {
     double current = PIL_check_seconds_timer();
 
     /* Time base quirky code to go around find-nearest slowness. */