GRID_HELPER: Filter targets based on dragging

Filtering based on selection ignores the use case where we are measuring
to a selected item.  This utilizes the dragged flag to prevent snapping
based on the current state of the item drag.

Fixes: lp:1801089
* https://bugs.launchpad.net/kicad/+bug/1801089

pcbnew/tools/edit_tool.cpp

@@ -438,6 +438,9 @@ int EDIT_TOOL::Main( const TOOL_EVENT& aEvent )
                         }
                     }
 
+                    for( auto item : selection )
+                        item->SetFlags( IS_DRAGGED ); //todo: flags structure rework
+
                     editFrame->UndoRedoBlock( true );
                     m_cursor = controls->GetCursorPosition();
 
@@ -558,6 +561,9 @@ int EDIT_TOOL::Main( const TOOL_EVENT& aEvent )
     if( unselect || restore_state )
         m_toolMgr->RunAction( PCB_ACTIONS::selectionClear, true );
 
+    for( auto item : selection )
+        item->ClearFlags( IS_DRAGGED ); //todo: flags structure rework
+
     if( restore_state )
         m_commit->Revert();
     else

pcbnew/tools/grid_helper.cpp

@@ -241,12 +241,11 @@ std::set<BOARD_ITEM*> GRID_HELPER::queryVisible( const BOX2I& aArea ) const
         BOARD_ITEM* item = static_cast<BOARD_ITEM*>( it.first );
 
         // The item must be visible and on an active layer
-        // It cannot be selected because this routine is used to calculate snapping,
-        // so the selected it is what we are snapping _from_ and should not be
-        // considered a snap target
+        // It cannot be moving as a moving item is being snapped _from_
+        // rather than considered a potential target
         if( view->IsVisible( item )
                 && ( !isHighContrast || activeLayers.count( it.second ) )
-                && !item->IsSelected() )
+                && !item->IsDragging() )
             items.insert ( item );
     }