Closes #19492 and fixes #19453

Documentation is giving an example that can be replaced by a more dry command.
Give a hint that ids can be used instead of pluck(:id).

[skip ci] Fix counter_cache in the Rails Guides

We don't actually need to enumerate the possible types here any more;
that dates back to before e105e599, when
they were symbols, and indistinguishable from other options.

Speedup String#squish

Merge branch 'action-mailer-async-doc-fixes' of https://github.com/mfazekas/rails into mfazekas-action-mailer-async-doc-fixes

Conflicts:
	actionmailer/lib/action_mailer/base.rb

Error message no longer tells you to set the (deprecated) secret_token.

[ci skip] Update contributing guide

remove reference to `register_javascript_expansion` and `register_stylesheet_expansion` from guide [ci skip]

remove reference to `register_javascript_expansion` and `register_stylesheet_expansion` from guide [ci skip]

These methods no longer exists.

Speed up Levenshtein by 50% and reduce 97% of memory usage

  Calculating -------------------------------------
             each_char   924.000  i/100ms
        each_codepoint     1.381k i/100ms
  -------------------------------------------------
             each_char      9.320k (¡Þ 5.1%) i/s -     47.124k
        each_codepoint     13.857k (¡Þ 3.6%) i/s -     70.431k

  Comparison:
        each_codepoint:    13857.4 i/s
             each_char:     9319.5 i/s - 1.49x slower

The full report can be found here:
  https://gist.github.com/yuki24/a80988f35aceac76f1d5

[ci skip] remove duplicate doc for current_page?

It was removed long ago: e358b1fc.

Missing note on validates_presence_of validation [ci skip]

Without this note, someone can misunderstand the usage of validates_presence_of method

add missing note for the validates_presence_of

Rename railties/bin to railties/exe to match the new Bundler convention

That will match the new Bundler executables convention.
Bundler Blog Post: http://bundler.io/blog/2015/03/20/moving-bins-to-exe.html
Also updated the necessary tests.

fix a wrong feature test method name

These methods were removed in cb9f7f48 and are no longer methods in the
Rails codebase.

[skip ci] primay_key -> primary_key

Merge branch 'belongs_to_primary_key_doc' of https://github.com/girishso/rails into girishso-belongs_to_primary_key_doc

[docs] Using the real resolver pattern in docs