Use TS::Cache instead plain Hash in TimeZone.

Plain ruby Hashes are not thread safe.
Unify AS::TZ's lazy init maps.

There's no point in having 2 almost identical (@lazy_zones_map and @zones_map) lazy initialized TZ instance caches.
Remove AS::TZ.lookup(name).

The method doesn't really make much sense (find_tzinfo will succeed for any imput provided).
Update render with a spacer_template [ci skip]
Merge pull request #13119 from sbagdat/patch-1

Update render with a spacer_template [ci skip]
Removed redundant field name in the guide 

Fixes: #13108
[ci skip]
Merge pull request #13121 from pftg/patch-1

Removed redundant field name in the guide
Honor to RAILS_GROUPS env variable while loading gems with Bundler
config.assets.enabled isn't used anymore to disable Rails asset pipeline
Merge pull request #11796 from thedarkone/time-zone-thread-safety

AS::TimeZone's cache thread safety
Use genderless pronouns in API docs
EscapedString is also private API [ci skip]
Merge pull request #13123 from chancancode/json_encoder_nodoc_fix

JSON encoder internals showed up in docs [ci skip]
Use .railsrc while creating new plugin if available

- Fixes #10700
Merge pull request #10712 from prathamesh-sonpatki/plugin-railsrc

Use .railsrc while creating new plugin if available. Fixes #10700
Use genderless pronouns in security guide. [ci skip]

related  #49ff20d9b164693ed7fee880b69cc14b141678b3
Merge pull request #13126 from vipulnsward/gender_neutral_pronouns

Use gender - neutral pronouns in security guide.
Introduce a context for rendering fixtures ERB.

Fixture files are passed through an ERB renderer before being read as
YAML. The rendering is currently done in the context of the main object,
so method definitons leak into other fixtures, and there is no clean
place to define fixture helpers.

After this commit, the ERB renderer will use a new subclass of
ActiveRecord::FixtureSet::RenderContext each time a fixture is rendered.