Only automatically include validations when enabled

This is a follow up to #16024.
Fix escape_once double-escaping hex-encoded entities

(This is a manual merge of #9102)
The hex escape sequence can be of any length
Add CHANGELOG for c803b90
Change the JSON renderer to enforce the 'JS' Content Type

The controller can set the response format as 'JSON' before the renderer code be
evaluated, so we must replace it when necessary.

Fixes #15081
Remove symbolized_path_parameters.

This pull request is a continuation of https://github.com/rails/rails/commit/925bd975 and https://github.com/rails/rails/commit/8d8ebe3d.
Merge pull request #16026 from lucasmazza/lm-respond-to-jsonp-fix

Change the JSON renderer to enforce the 'JS' Content Type
Add `:all` argument to `count` in `reset_counters`

Prior to this fix, if an association had a scope with a `select`,
calls to `reset_counters` would generate invalid SQL and throw:

ActiveRecord::StatementInvalid: [$DB_ADAPTER]: wrong number of
arguments to function COUNT()

References #10710, #13648
Fix typo in comment
Explicitly call #to_s when serializing GlobalID. Addresses #95
Merge pull request #16029 from cade/fix_typo_in_comment

Fix typo in comment
Merge pull request #15941 from variousred/docrails-changes

[ci skip] Changes some wording to better foreshadow what is coming up later
Use the type object for type casting HStore columns
Do not rely on the column type when quoting infinity
Merge pull request #16034 from sgrif/sg-hstore-type-object

Use the type object for type casting HStore columns
Merge pull request #16036 from sgrif/sg-datetime-infinity

Do not rely on the column type when quoting infinity
Fix guide. sample code syntax error.[ci skip]
Merge pull request #16038 from tbpgr/fix_guide_active_record_validations

Fix guide. sample code syntax error.[ci skip]
require 'resque-scheduler' fix #97
Merge pull request #98 from seuros/resque

Require correct file for resque scheduler