Add object type checks in `OB_MODE_SCULPT` for Mesh vs. GreasePencil.

This may be split up again for review, but developing shared sculpt
utilities for GPv3 tools is easier this way.

@@ -0,0 +62,4 @@
+      return {};
+    }
+    const Layer &active_layer = *grease_pencil.get_active_layer();
+    Drawing *drawing = grease_pencil.get_editable_drawing_at(active_layer, scene.r.cfra);

@@ -0,0 +75,4 @@
+  }
+
+  /* Apply to all editable drawings. */
+  return ed::greasepencil::retrieve_editable_drawings(scene, grease_pencil);

@@ -0,0 +44,4 @@
+  return mouse_delta;
+}
+
+Vector<ed::greasepencil::MutableDrawingInfo> get_drawings_for_sculpt(const bContext &C)

@@ -0,0 +54,4 @@
+
+    selection.foreach_index(GrainSize(4096), [&](const int64_t point_i) {
+      float &radius = radii[point_i];
+      const float influence = brush_influence(*CTX_data_scene(&params.context),

@@ -4696,0 +4696,4 @@
+        # Invoke sculpt operator
+        ("grease_pencil.sculpt_paint", {"type": 'LEFTMOUSE', "value": 'PRESS'}, None),
+        ("grease_pencil.sculpt_paint", {"type": 'LEFTMOUSE', "value": 'PRESS',
+         "ctrl": True}, {"properties": [("mode", 'INVERT')]}),        # # Selection

@@ -2440,0 +2391,4 @@
+    clipboard.curves = {};
+    clipboard.materials.clear_and_shrink();
+    clipboard.materials_in_source_num = 0;
+    MEM_delete(grease_pencil_clipboard);

@@ -0,0 +45,4 @@
+{
+  /* Note: GPv2 method, this does not return a different value for every invocation: the time-based
+   * part remains the same for one second and the pointer isn't guaranteed to be different. */
+  //   unsigned int seed = (unsigned int)(BLI_time_now_seconds_i() & UINT_MAX);

@@ -0,0 +128,4 @@
+      changed = true;
+    }
+    if (sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_UV) {
+      /* TODO stroke_u attribute not used yet. */

@@ -0,0 +112,4 @@
+      changed = true;
+    }
+    if (sculpt_mode_flag & GP_SCULPT_FLAGMODE_APPLY_UV) {
+      /* TODO stroke_u attribute not used yet. */

@@ -476,0 +507,4 @@
+                                                        toolsettings->gp_sculpt.cur_falloff) :
+                                1.0f;
+      editable_drawings.append(
+          {*drawing, layer.drawing_index_at(frame_number), frame_number, falloff});

@@ -0,0 +91,4 @@
+                               (use_pressure ? sample.pressure : 1.0f);
+
+  /* Distance falloff. */
+  const int2 mval_i = int2(math::round(sample.mouse_position));

@@ -0,0 +135,4 @@
+    const float influence = influence_base * brush_falloff;
+
+    if (influence > 0.0f) {
+      indices.append(point_i);

@@ -0,0 +26,4 @@
+/* Use a hash to generate random numbers. */
+static float hash_rng(unsigned int seed1, unsigned int seed2, int index)
+{
+  return BLI_hash_int_01(BLI_hash_int_3d(seed1, seed2, (unsigned int)index));

@@ -139,3 +136,1 @@
-        total_weight[index] += w - w2;
-        dst[index] = src[index] + influence * dst[index] / total_weight[index];
-      }
+  auto mix_smoothed = [&](const int index, const float influence) {

@@ -0,0 +88,4 @@
+  /* Basic strength factor from brush settings. */
+  const bool use_pressure = (brush.gpencil_settings->flag & GP_BRUSH_USE_PRESSURE);
+  const float influence_base = brush.alpha * multi_frame_falloff *
+                               (use_pressure ? sample.pressure : 1.0f);

@@ -0,0 +117,4 @@
+  const float radius_squared = radius * radius;
+  const bool use_pressure = (brush.gpencil_settings->flag & GP_BRUSH_USE_PRESSURE);
+  const float influence_base = brush.alpha * multi_frame_falloff *
+                               (use_pressure ? pressure : 1.0f);

@@ -0,0 +147,4 @@
+{
+  /* The basic setting is the brush's setting. */
+  bool invert = ((brush.gpencil_settings->sculpt_flag & GP_SCULPT_FLAG_INVERT) != 0) ||
+                (brush.gpencil_settings->sculpt_flag & BRUSH_DIR_IN);

@@ -0,0 +135,4 @@
+
+  IndexMask index_mask = IndexMask::from_predicate(
+      selection, GrainSize(4096), memory, [&](const int point_i) {
+        const float influence = calculate_influence(point_i);

@@ -0,0 +94,4 @@
+                                   BKE_brush_alpha_get(&scene, &brush) :
+                                   1.0f;
+  const float influence_base = brush_pressure * multi_frame_falloff *
+                               (use_pressure ? sample.pressure : 1.0f);

@@ -0,0 +126,4 @@
+                                   BKE_brush_alpha_get(&scene, &brush) :
+                                   1.0f;
+  const float influence_base = brush_pressure * multi_frame_falloff *
+                               (use_pressure ? pressure : 1.0f);