Compositor: add button to add a new texture in the Texture node

This replaces the plain texture selector with a proper TemplateID,
resulting in buttons to add a new texture if none is there yet, and if
there is one, there will be the usual conveniece buttons to add a fake
user, create single user copies, ..., as well as the button to go to the
textures tab in the Properties Editor for more fine-grained control over
the texture.

Fixes #126856

Pull Request: https://projects.blender.org/blender/blender/pulls/126890

source/blender/editors/space_node/drawnode.cc

@@ -198,14 +198,23 @@ static void node_buts_normal(uiLayout *layout, bContext * /*C*/, PointerRNA *ptr
   uiItemR(layout, &sockptr, "default_value", DEFAULT_FLAGS, "", ICON_NONE);
 }
 
-static void node_buts_texture(uiLayout *layout, bContext * /*C*/, PointerRNA *ptr)
+static void node_buts_texture(uiLayout *layout, bContext *C, PointerRNA *ptr)
 {
   bNode *node = (bNode *)ptr->data;
 
   short multi = (node->id && ((Tex *)node->id)->use_nodes && (node->type != CMP_NODE_TEXTURE) &&
                  (node->type != TEX_NODE_TEXTURE));
 
-  uiItemR(layout, ptr, "texture", DEFAULT_FLAGS, "", ICON_NONE);
+  uiTemplateID(layout,
+               C,
+               ptr,
+               "texture",
+               "texture.new",
+               nullptr,
+               nullptr,
+               UI_TEMPLATE_ID_FILTER_ALL,
+               false,
+               nullptr);
 
   if (multi) {
     /* Number Drawing not optimal here, better have a list. */