[1.1.x] Fix for G2/G3 rounding error (MarlinFirmware#15546)

Marlin/Marlin_main.cpp

@@ -3707,7 +3707,8 @@ inline void gcode_G0_G1(
           const float e = clockwise ^ (r < 0) ? -1 : 1,             // clockwise -1/1, counterclockwise 1/-1
                       dx = p2 - p1, dy = q2 - q1,                   // X and Y differences
                       d = HYPOT(dx, dy),                            // Linear distance between the points
-                      h = SQRT(sq(r) - sq(d * 0.5f)),               // Distance to the arc pivot-point
+                      h2 = (r - 0.5f * d) * (r + 0.5f * d),         // factor to reduce rounding error
+                      h = (h2 >= 0) ? SQRT(h2) : 0.0f,              // Distance to the arc pivot-point
                       mx = (p1 + p2) * 0.5f, my = (q1 + q2) * 0.5f, // Point between the two points
                       sx = -dy / d, sy = dx / d,                    // Slope of the perpendicular bisector
                       cx = mx + e * h * sx, cy = my + e * h * sy;   // Pivot-point of the arc