fix(@nestjs/swagger): replace quoted functionPlaceholder completely

When building JS InitOptions, functions get replaced by a placeholder.
JSON.stringify quotes strings, so we need to replace the placeholder
including the quotes.

Fixes:  #1962

lib/swagger-ui/helpers.ts

@@ -18,7 +18,7 @@ export function buildJSInitOptions(initOptions: SwaggerUIInitOptions) {
     2
   );
 
-  json = json.replace(new RegExp(functionPlaceholder, 'g'), () => fns.shift());
+  json = json.replace(new RegExp('"' + functionPlaceholder + '"', 'g'), () => fns.shift());
 
   return `let options = ${json};`;
 }