UI: Consistent Area Move Snapping Locations

Change Area Move snapping locations to even 12ths, rather than current
eights and thirds, so snap distances are consistent sizes. Also adds
snapping at minimum and maximum locations.

see D11938 for details and illustrations.

Differential Revision: https://developer.blender.org/D11938

Reviewed by Hans Goudey

source/blender/editors/screen/screen_ops.c

@@ -1738,19 +1738,19 @@ static int area_snap_calc_location(const bScreen *screen,
       int snap_dist_best = INT_MAX;
       {
         const float div_array[] = {
-            /* Middle. */
-            1.0f / 2.0f,
-            /* Thirds. */
-            1.0f / 3.0f,
-            2.0f / 3.0f,
-            /* Quarters. */
-            1.0f / 4.0f,
-            3.0f / 4.0f,
-            /* Eighth. */
-            1.0f / 8.0f,
-            3.0f / 8.0f,
-            5.0f / 8.0f,
-            7.0f / 8.0f,
+            0.0f,
+            1.0f / 12.0f,
+            2.0f / 12.0f,
+            3.0f / 12.0f,
+            4.0f / 12.0f,
+            5.0f / 12.0f,
+            6.0f / 12.0f,
+            7.0f / 12.0f,
+            8.0f / 12.0f,
+            9.0f / 12.0f,
+            10.0f / 12.0f,
+            11.0f / 12.0f,
+            1.0f,
         };
         /* Test the snap to the best division. */
         for (int i = 0; i < ARRAY_SIZE(div_array); i++) {