Don't do a full connection database reset on HardRedraw()

Only update the intersheet references to avoid the penalty of
connectivity re-calculations on each redraw

Cherry-picked from b8ee588a76 and 08c2828bd3

eeschema/sch_edit_frame.cpp

@@ -614,7 +614,8 @@ void SCH_EDIT_FRAME::SetCurrentSheet( const SCH_SHEET_PATH& aSheet )
 
 void SCH_EDIT_FRAME::HardRedraw()
 {
-    RecalculateConnections( LOCAL_CLEANUP );
+    if( Schematic().Settings().m_IntersheetRefsShow )
+        RecomputeIntersheetRefs();
 
     FocusOnItem( nullptr );