SCH_COMMIT: when clearing all item flags, do not clear SELECTED item flags.

If a item is selected, its SELECTED flag cannot be cleared without managing
selections stored in tools, and must be still selected after changes.
Fixes #15671
https://gitlab.com/kicad/code/kicad/-/issues/15671

eeschema/sch_commit.cpp

@@ -302,7 +302,10 @@ void SCH_COMMIT::pushSchEdit( const wxString& aMessage, int aCommitFlags )
             break;
         }
 
-        schItem->ClearFlags();
+        // Clear all flags but SELECTED, after edition
+        // (selected items must keep their selection flag).
+        const int selected_mask = ( SELECTED | SELECTED_BY_DRAG );
+        schItem->ClearFlags( EDA_ITEM_ALL_FLAGS - selected_mask );
     }
 
     if( schematic )