GPv3: Set selected curve material as active material

This operator assigns the material of the first selected curve as
active material.

@@ -951,0 +960,4 @@
+  GreasePencil &grease_pencil = *static_cast<GreasePencil *>(object->data);
+  bool changed = false;
+  grease_pencil.foreach_editable_drawing(
+      scene->r.cfra, [&](int /*drawing_index*/, bke::greasepencil::Drawing &drawing) {

@@ -240,2 +240,3 @@
     if constexpr (std::is_same_v<T, float> || std::is_same_v<T, float2> ||
-                  std::is_same_v<T, float3>) {
+                  std::is_same_v<T, float3>)
+    {

@@ -812,3 +813,3 @@
 
   grease_pencil.foreach_editable_drawing(
-      scene->r.cfra, [&](int /*drawing_index*/, bke::greasepencil::Drawing &drawing) {
+      scene->r.cfra, [&](int /*layer_index*/, bke::greasepencil::Drawing &drawing) {

@@ -951,0 +971,4 @@
+        if (selected_curves.is_empty()) {
+          return;
+        }
+        const blender::VArray<int> materials = *curves.attributes().lookup_or_default<int>(

@@ -951,0 +974,4 @@
+        const blender::VArray<int> materials = *curves.attributes().lookup_or_default<int>(
+            "material_index", ATTR_DOMAIN_CURVE, -1);
+
+        selected_curves.foreach_index([&](const int curve_index) {

@@ -951,0 +975,4 @@
+            "material_index", ATTR_DOMAIN_CURVE, -1);
+
+        selected_curves.foreach_index([&](const int curve_index) {
+          if (materials[curve_index] != -1) {

@@ -951,0 +973,4 @@
+        const blender::VArray<int> materials = *curves.attributes().lookup_or_default<int>(
+            "material_index", ATTR_DOMAIN_CURVE, 0);
+        if (object->totcol > 0) {
+          object->actcol = materials[selected_curves.first()] + 1;

@@ -951,0 +976,4 @@
+          object->actcol = materials[selected_curves.first()] + 1;
+        }
+        changed = true;
+        return;

@@ -960,0 +983,4 @@
+    }
+  };
+
+  WM_event_add_notifier(C, NC_GEOM | ND_DATA | NA_EDITED, &grease_pencil);

@@ -960,0 +973,4 @@
+
+    IndexMaskMemory memory;
+    IndexMask selected_curves = ed::curves::retrieve_selected_curves(curves, memory);
+    if (!selected_curves.is_empty()) {

@@ -960,0 +976,4 @@
+    if (!selected_curves.is_empty()) {
+      const blender::VArray<int> materials = *curves.attributes().lookup_or_default<int>(
+          "material_index", ATTR_DOMAIN_CURVE, 0);
+      if (object->totcol > 0) {