Merge pull request #14908 from bdunne/deprecate_gemfile_dev_rb

It's time to deprecate Gemfile.dev.rb

Gemfile

@@ -159,7 +159,10 @@ end
 #   developers may not need or may not easily install, such as rails-dev-boost,
 #   any git based gem, and compiled gems like rbtrace or memprof.
 dev_gemfile = File.expand_path("Gemfile.dev.rb", __dir__)
-eval_gemfile(dev_gemfile) if File.exist?(dev_gemfile)
+if File.exist?(dev_gemfile)
+  Bundler::UI::Shell.new.warn "** Gemfile.dev.rb deprecated, please move it to bundler.d/"
+  eval_gemfile(dev_gemfile)
+end
 
 # Load other additional Gemfiles
 Dir.glob("bundler.d/*.rb").each { |f| eval_gemfile(File.expand_path(f, __dir__)) }