Remove use of reflection in MustacheViewResolver

Prior to this commit the MustacheViewResolver used reflection
to instantiate a MustacheView class, which fails when using AOT.
Creating the view without reflection (analogous to the
FreemarkerViewResolver) will fix this without the need for additional
constructor hints.

See gh-32030

Author: mdeinum

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/reactive/result/view/MustacheViewResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2022 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -27,6 +27,7 @@
  * Spring WebFlux {@link ViewResolver} for Mustache.
  *
  * @author Brian Clozel
+ * @author Marten Deinum
  * @since 2.0.0
  */
 public class MustacheViewResolver extends UrlBasedViewResolver {
@@ -75,4 +76,9 @@ protected AbstractUrlBasedView createView(String viewName) {
 		return view;
 	}
 
+	@Override
+	protected AbstractUrlBasedView instantiateView() {
+		return (getViewClass() == MustacheView.class) ? new MustacheView() : super.instantiateView();
+	}
+
 }