Add more load hooks to Rails/ActiveSupportOnLoad

[Earlopain]

Mostly from Rails 7.1, except for active_record_sqlite3adapter which has been around for longer but wasn't documented until recently.

Reference list: https://guides.rubyonrails.org/engines.html#available-load-hooks

Rails PRs:

• ActiveRecord::TestFixtures/active_record_fixtures: Run a load hook when TestFixtures is included rails/rails#47690
• ActiveModel::Model/active_model: Add a load hook for ActiveModel::Model rails/rails#48698
• ActionText::EncryptedRichText/action_text_encrypted_rich_text: Add ActiveSupport load hook for ActionText::EncryptedRichText rails/rails#47737 7.1
• ActiveRecord::ConnectionAdapters::PostgreSQLAdapter/active_record_postgresqladapter: Add timestamptz as a time zone aware type for PostgreSQL rails/rails#44601
• ActiveRecord::ConnectionAdapters::Mysql2Adapter/active_record_mysql2adapter: Add load hook for ActiveRecord::ConnectionAdapters::Mysql2Adapter rails/rails#48012
• ActiveRecord::ConnectionAdapters::TrilogyAdapter/active_record_trilogyadapter: Clean up docs and code using mysql2 when we mean trilogy rails/rails#48175

For active_record_sqlite3adapter:
Functionality introduced with rails/rails#29699, docs only added with rails/rails#48012

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Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.
• If this is a new cop, consider making a corresponding update to the Rails Style Guide.

[koic]

Thanks!