Patch G29 for 3-point leveling

Marlin/Conditionals_post.h

       #define AUTO_BED_LEVELING_NONLINEAR
     #else
       #define AUTO_BED_LEVELING_LINEAR
+      #define AUTO_BED_LEVELING_LINEAR_GRID
     #endif
   #endif
 

Marlin/Marlin_main.cpp

   #include "vector_3.h"
 #endif
 
-#if ENABLED(AUTO_BED_LEVELING_LINEAR)
+#if ENABLED(AUTO_BED_LEVELING_LINEAR_GRID)
   #include "qr_solve.h"
 #elif ENABLED(MESH_BED_LEVELING)
   #include "mesh_bed_leveling.h"
         float zoffset = zprobe_zoffset;
         if (code_seen('Z')) zoffset += code_value_axis_units(Z_AXIS);
 
-      #elif ENABLED(AUTO_BED_LEVELING_LINEAR)
+      #elif ENABLED(AUTO_BED_LEVELING_LINEAR_GRID)
 
         /**
          * solve the plane equation ax + by + d = z
                mean = 0.0;
         int indexIntoAB[abl_grid_points_x][abl_grid_points_y];
 
-      #endif // AUTO_BED_LEVELING_LINEAR
+      #endif // AUTO_BED_LEVELING_LINEAR_GRID
 
       int probePointCounter = 0;
       bool zig = abl_grid_points_y & 1; //always end at [RIGHT_PROBE_BED_POSITION, BACK_PROBE_BED_POSITION]
 
           measured_z = probe_pt(xProbe, yProbe, stow_probe_after_each, verbose_level);
 
-          #if ENABLED(AUTO_BED_LEVELING_LINEAR)
+          #if ENABLED(AUTO_BED_LEVELING_LINEAR_GRID)
 
             mean += measured_z;
             eqnBVector[probePointCounter] = measured_z;
       if (!dryrun) extrapolate_unprobed_bed_level();
       print_bed_level();
 
-    #elif ENABLED(AUTO_BED_LEVELING_LINEAR)
+    #elif ENABLED(AUTO_BED_LEVELING_LINEAR_GRID)
 
       // For LINEAR leveling calculate matrix, print reports, correct the position
 
         }
       } //do_topography_map
 
+    #endif // AUTO_BED_LEVELING_LINEAR_GRID
+
+    #if ENABLED(AUTO_BED_LEVELING_LINEAR)
+
       // For LINEAR and 3POINT leveling correct the current position
 
       if (verbose_level > 0)
             float xydiff[2] = { offset_vec.x, offset_vec.y };
             current_position[Z_AXIS] += offset_vec.z;
 
-          #else // !AUTO_BED_LEVELING_FEATURE
+          #else // !AUTO_BED_LEVELING_LINEAR
 
             float xydiff[2] = {
               hotend_offset[X_AXIS][tmp_extruder] - hotend_offset[X_AXIS][active_extruder],

Marlin/qr_solve.cpp

 
 #include "qr_solve.h"
 
-#if ENABLED(AUTO_BED_LEVELING_LINEAR)
+#if ENABLED(AUTO_BED_LEVELING_LINEAR_GRID)
 
 #include <stdlib.h>
 #include <math.h>