Render objects that respond_to render_in in controllers

In https://github.com/rails/rails/pull/36388,
we supported passing objects that `respond_to` `render_in`
to `render`, but _only_ in views.

This change does the same for controllers, as Rails
generally gives the expectation that `render` behaves
the same in both contexts.

Co-authored-by: Aaron Patterson <tenderlove@github.com>

actionpack/test/lib/test_component.rb

@@ -10,9 +10,6 @@ class TestComponent < ActionView::Base
     @title = title
   end
 
-  # Entrypoint for rendering. Called by ActionView::RenderingHelper#render.
-  #
-  # Returns ActionView::OutputBuffer.
   def render_in(view_context)
     self.class.compile
     @view_context = view_context
@@ -20,6 +17,10 @@ class TestComponent < ActionView::Base
     rendered_template
   end
 
+  def format
+    :html
+  end
+
   def self.template
     <<~'erb'
     <span title="<%= title %>">(<%= render(plain: "Inline render") %>)</span>

actionview/lib/action_view/renderer/renderer.rb

@@ -25,6 +25,9 @@ module ActionView
     def render_to_object(context, options) # :nodoc:
       if options.key?(:partial)
         render_partial_to_object(context, options)
+      elsif options.key?(:object)
+        object = options[:object]
+        AbstractRenderer::RenderedTemplate.new(object.render_in(context), object)
       else
         render_template_to_object(context, options)
       end

actionview/lib/action_view/rendering.rb

@@ -144,6 +144,8 @@ module ActionView
         else
           if action.respond_to?(:permitted?) && action.permitted?
             options = action
+          elsif action.respond_to?(:render_in)
+            options[:object] = action
           else
             options[:partial] = action
           end