Mask Editor: Add toggle for mask spline drawing

Adds an overlay option to show/hide the spline points & lines of masks in the Mask Editor.

It also moves the "smooth" option up (its position left of the selection dropdown was missleading).

{F11847272}

This emerged from a discussion in https://developer.blender.org/D12776

Differential Revision: https://developer.blender.org/D13314

source/blender/blenkernel/BKE_blender_version.h

@@ -25,7 +25,7 @@ extern "C" {
 
 /* Blender file format version. */
 #define BLENDER_FILE_VERSION BLENDER_VERSION
-#define BLENDER_FILE_SUBVERSION 2
+#define BLENDER_FILE_SUBVERSION 3
 
 /* Minimum Blender version that supports reading file written with the current
  * version. Older Blender versions will test this and show a warning if the file