Port gp legacy "invert weight" operator.

@@ -360,0 +379,4 @@
+    /* Active vgroup index of drawing. */
+    const int drawing_vgroup_index = BLI_findstringindex(
+        &curves.vertex_group_names, active_defgroup->name, offsetof(bDeformGroup, name));
+

@@ -360,0 +387,4 @@
+      return;
+    }
+
+    for (int i : weights.index_range()) {

@@ -360,0 +371,4 @@
+
+  const bDeformGroup *active_defgroup = static_cast<const bDeformGroup *>(
+      BLI_findlink(BKE_object_defgroup_list(object), active_index));
+

@@ -360,0 +379,4 @@
+    /* Active vgroup index of drawing. */
+    const int drawing_vgroup_index = BLI_findstringindex(
+        &curves.vertex_group_names, active_defgroup->name, offsetof(bDeformGroup, name));
+    BLI_assert(drawing_vgroup_index != -1);

@@ -360,0 +389,4 @@
+    }
+
+    for (const int i : weights.index_range()) {
+      const float invert_weight = 1 - weights[i];

@@ -360,0 +408,4 @@
+
+  /* api callbacks */
+  ot->exec = grease_pencil_weight_invert_exec;
+  ot->poll = grease_pencil_weight_painting_poll;