Gizmo: Support translation without cross drawing

Add an enum entry `ED_GIZMO_CAGE_DRAW_FLAG_NOP` to be able to set enums
explicitly to draw no handles.
The current code already supports this case implicitly.

See https://projects.blender.org/blender/blender/pulls/139107 for an
example use case.

Pull Request: https://projects.blender.org/blender/blender/pulls/139210

source/blender/editors/gizmo_library/gizmo_types/cage2d_gizmo.cc

@@ -953,6 +953,10 @@ static int gizmo_cage2d_test_select(bContext *C, wmGizmo *gz, const int mval[2])
       r.ymin = -size[1] + margin[1];
       r.xmax = size[0] - margin[0];
       r.ymax = size[1] - margin[1];
+      if (!BLI_rctf_is_valid(&r)) {
+        /* Typically happens when gizmo width or height is very small. */
+        BLI_rctf_sanitize(&r);
+      }
     }
     bool isect = BLI_rctf_isect_pt_v(&r, point_local);
     if (isect) {

source/blender/editors/include/ED_gizmo_library.hh

@@ -119,6 +119,7 @@ enum {
 
 /* draw_options */
 enum {
+  ED_GIZMO_CAGE_DRAW_FLAG_NOP = 0,
   /** Draw a central handle (instead of having the entire area selectable)
    * Needed for large rectangles that we don't want to swallow all events. */
   ED_GIZMO_CAGE_DRAW_FLAG_XFORM_CENTER_HANDLE = (1 << 0),