Follow up to #16613

Since we want this flag to be enabled anytime we are running the tests
under JRuby, let's enable this at the Rakefile level so people get the
performance boost on their local checkout.

Moreover, we avoid having to update this particular line anytime the
option changes on the JRuby side.

The only drawback is that we have to define it in every Rakefile but
there's no big deal, this is already the case for other options.
Added processing of `nil` to `highlight` helper method
Refactor callback setup in to use lambda instead of eval
Merge pull request #17114 from pabloh/replace_use_of_eval_with_lambda

Refactor callback setup to use lambda instead of eval
Merge pull request #17113 from igor04/helpers-highlight

Added processing of `nil` to `highlight` helper method
In render file, by default the current layout is rendered always
Merge pull request #17124 from yuktikhurana/fix_render_file_guide

In render file, by default the current layout is rendered always [ci skip]
use tr instead of gsub when possible
Merge pull request #17125 from acrogenesis/master

use tr instead of gsub when possible
Merge pull request #17088 from robin850/jruby-dev

Follow up to #16613