Move ExtUI ABL mesh edit, limit to bilinear (MarlinFirmware#20381)

* Move ExtUI call

Co-authored-by: Scott Lahteine <github@thinkyhead.com>
Co-authored-by: Victor Mateus Oliveira <rhapsodyv@gmail.com>
Co-authored-by: Sebastiaan Dammann <sebastiaandammann@outlook.com>

Marlin/src/gcode/bedlevel/abl/G29.cpp

@@ -177,8 +177,6 @@ G29_TYPE GcodeSuite::G29() {
     if (DISABLED(PROBE_MANUALLY) && seenQ) G29_RETURN(false);
   #endif
 
-  TERN_(EXTENSIBLE_UI, ExtUI::onMeshLevelingStart());
-
   const bool seenA = TERN0(PROBE_MANUALLY, parser.seen('A')),
          no_action = seenA || seenQ,
               faux = ENABLED(DEBUG_LEVELING_FEATURE) && DISABLED(PROBE_MANUALLY) ? parser.boolval('C') : no_action;
@@ -399,6 +397,10 @@ G29_TYPE GcodeSuite::G29() {
       points[0].z = points[1].z = points[2].z = 0;  // Probe at 3 arbitrary points
     #endif
 
+    #if BOTH(AUTO_BED_LEVELING_BILINEAR, EXTENSIBLE_UI)
+      ExtUI::onMeshLevelingStart();
+    #endif
+
     if (!faux) remember_feedrate_scaling_off();
 
     // Disable auto bed leveling during G29.