Fix #139126: Paint: Undo in Texture Paint mode does not redraw object

This was a case of missing relation tagging update.
The update was functional only after something else
tagged relations.

The relation update needed to be added in both the
Image texture node RNA function (for manually changed
images) and in the add painting slot operator.

Pull Request: https://projects.blender.org/blender/blender/pulls/140270

source/blender/editors/sculpt_paint/paint_image_proj.cc

@@ -6809,6 +6809,7 @@ static bool proj_paint_add_slot(bContext *C, wmOperator *op)
 
     DEG_id_tag_update(&ntree->id, 0);
     DEG_id_tag_update(&ma->id, ID_RECALC_SHADING);
+    DEG_relations_tag_update(bmain);
     ED_area_tag_redraw(CTX_wm_area(C));
 
     ED_paint_proj_mesh_data_check(*scene, *ob, nullptr, nullptr, nullptr, nullptr);

source/blender/makesrna/intern/rna_nodetree.cc

@@ -3126,6 +3126,7 @@ static void rna_Node_tex_image_update(Main *bmain, Scene * /*scene*/, PointerRNA
 
   BKE_ntree_update_tag_node_property(ntree, node);
   BKE_main_ensure_invariants(*bmain, ntree->id);
+  DEG_relations_tag_update(bmain);
   WM_main_add_notifier(NC_IMAGE, nullptr);
 }