Allow theme updates via SVN

[dd32]

As mentioned in ​the recent results of the Theme Upload survey we're going to open up SVN commit for theme authors to update themes.

This will (at least initially) have certain restrictions on the format of the commits by Theme Authors, so as to keep the changes required to the Theme Directory to a minimum and avoid disruption for authors.

This is a tracking ticket for the changes needed on WordPress.org for this.

For general discussion and feedback related to this project, please kindly keep the discussion on ​https://make.wordpress.org/themes/2021/09/13/theme-upload-survey-results-next-steps/ so as to keep all feedback in a single centralised location. Issues that arise due to changes in this ticket can be logged here comment, or if this ticket is closed, as a new meta ticket.

[dd32]

In 11228:

Theme Directory: Add an API endpoint to generate a dynamic SVN auth file.

Note: This won't take effect until we're ready to welcome commits.

See #5899.

[dd32]

In 11229:

Theme Directory: Add a method to import a theme update from a SVN directory.

See #5899.

[dd32]

In 11230:

Theme Directory: Move exec_with_notify() to a trait for use in other classes too.

See #5899.

[dd32]

In 11231:

Theme Directory: Move exec_with_notify() to a trait for use in other classes too.

Take two.

See #5899.

[dd32]

In 11232:

Theme Directory: Add a cron task to monitor themes.svn.wordpress.org for new commits.

See #5899.

[dd32]

In 11233:

Theme Directory: Remove some debug that slipped into [11232].

See #5899/

[dd32]

In 11237:

Theme Directory: Introduce a specific constant/key for fetching the SVN Auth file.

This also stops outputting theme access rules until ready.

See #5899.

[dd32]

Just noting that further implementation is awaiting systems implementation.

​https://make.wordpress.org/systems/2021/09/17/theme-directory-changes/