Make ResolverDecorator a subclass of ActionView::Resolver

Follows
rails/rails@e65d41a.

ActionView::PathSet now rejects resolvers unless they inherit from
ActionView::Resolver, so ResolverDecorator must do so. By removing all
inherited methods, we ensure that method_missing will still intercept
all method calls.

Co-authored-by: Iliana Hadzhiatanasova <me@iliana.dev>

lib/rspec/rails/view_rendering.rb

@@ -71,7 +71,15 @@ def self.template_format(template)
         # templates with modified source
         #
         # @private
-        class ResolverDecorator
+        class ResolverDecorator < ::ActionView::Resolver
+          (::ActionView::Resolver.instance_methods - Object.instance_methods).each do |method|
+            undef_method method
+          end
+
+          (::ActionView::Resolver.methods - Object.methods).each do |method|
+            singleton_class.undef_method method
+          end
+
           def initialize(resolver)
             @resolver = resolver
           end