(fix) correct mappings for reactive declarations

By using `appendRight` the source mappings are correct and we get proper autocompletion suggestions inside reactive statements, too

Author: dummdidumm

packages/svelte2tsx/src/svelte2tsx/processInstanceScriptContent.ts

@@ -438,7 +438,7 @@ export function processInstanceScriptContent(
                 const end = node.getEnd() + astOffset;
 
                 str.prependLeft(start, ';() => {');
-                str.prependRight(end, '}');
+                str.appendRight(end, '}');
             }
         }