Separate LIB_PIN and SCH_PIN GetShownName/Number processing.

SCH_PIN wasn't handling the legacy empty string token (~), but
more importantly this will allow text variable resolution specific
to the schematic.

Fixes https://gitlab.com/kicad/code/kicad/issues/8625

eeschema/tools/backannotate.cpp

@@ -531,7 +531,7 @@ void BACK_ANNOTATE::processNetNameChange( const wxString& aRef, SCH_PIN* aPin,
 
         msg.Printf( _( "Change %s pin %s net label from '%s' to '%s'." ),
                     aRef,
-                    aPin->GetNumber(),
+                    aPin->GetShownNumber(),
                     aOldName,
                     aNewName );
 
@@ -554,15 +554,19 @@ void BACK_ANNOTATE::processNetNameChange( const wxString& aRef, SCH_PIN* aPin,
 
         if( schPin->IsPowerConnection() )
         {
-            msg.Printf( _( "Net %s cannot be changed to '%s' because it is driven by a power "
-                           "pin." ), aOldName, aNewName );
+            msg.Printf( _( "Net %s cannot be changed to %s because it is driven by a power pin." ),
+                        aOldName,
+                        aNewName );
 
             m_reporter.ReportHead( msg, RPT_SEVERITY_ERROR );
             break;
         }
 
         ++m_changesCount;
-        msg.Printf( _( "Add label '%s' to %s pin %s net." ), aNewName, aRef, aPin->GetNumber() );
+        msg.Printf( _( "Add label '%s' to %s pin %s net." ),
+                    aNewName,
+                    aRef,
+                    aPin->GetShownNumber() );
 
         if( !m_dryRun )
         {