Modify TimeWithZone#as_json to return 3DP of sub-second accuracy by default, since it's allowed by the spec and is very useful.
ruby constant syntax is not supported as routing `:controller` option.

The current implementation only works correctly if you supply the `:controller`
with directory notation (eg. `:controller => 'admin/posts'`).

The ruby constant notation (eg. `:controller => 'Admin::Posts`) leads to unexpected problems with `url_for`.

This patch prints a warning for every non supported `:controller` option. I also added documentation how
to work with namespaced controllers. The warning links to that documentation in the rails guide.
Merge pull request #9039 from senny/warn_on_controller_option_with_ruby_constant_syntax

ruby constant syntax is not supported as routing `:controller` option.
Update actionpack/CHANGELOG.md

[ci skip]
Merge pull request #9128 from jamesotron/iso8601-sub-second-accuracy

Modify TimeWithZone#as_json to return 3DP of sub-second accuracy.
Update changelog from #9128 with author name

And improve AS changelog a bit [ci skip]
Add some tests to enumerate how extensions should be stored in the schema output
improve tests to check for existence of extensions method, and skip testing dumped extensions if they are unsupported by the database
add ActiveRecord::AbstractAdapter#extensions and ActiveRecord::ConnectionAdapters::PostgreSQLAdapter#extensions to allow dumping of enabled extensions to schema.rb, add ActiveRecord::SchemaDumper#extensions to dump extensions to schema.rb
Merge pull request #9203 from jaggederest/dumping_pgsql_extensions

Adding database extension support to schema.rb
Add changelog entry for #9203 about schema dumper with db extensions

[ci skip]
Call super to use the abstract adapter implementation instead
Fix indentation of extensions in schema
Add blank line after extensions to separate from tables in schema
Do not print anything related to extensions when they don't none exist

When extensions are supported but there's no one enabled in the
database, we should not print anything related to them in schema.rb.
Run schema dumper extensions without creating real extensions

There is no need to create the extension in the database just to test if
it's dumped, we can stub that instead.