Content Parsers: Update parsers, fix list-item parsing, fix broken manifest

[ryelle]

This PR updates the parsers using the code added in WordPress/wordpress.org#90, and adds a phpunit env and tests for the parser.

I wanted to fix the list issue #211 so that it didn't require a manual update each time build:patterns was run, and I've had this branch half-done for a while in the wporg-mu-plugins repo, but it seems faster to iterate on the parsers here.

This is probably easier to review going commit-by-commit:

• 12fb450 — Update the parsers
• 66e32b0 — Add phpunit environment (copied from Add export content parsers tests #181)
• e52327d — Remove the broken swag page from the manifest, this was preventing all following pages from exporting
• 88409ce — Run build:patterns with the new content
• f57089a — Add phpunit step to the github workflows

Fixes #179, closes #181, fixes #211.

Props @adamwoodnz @dd32 for most of the code, I've just moved it around 🙂

How to test the changes in this Pull Request:

1. Run composer update to get the latest packages
2. Run yarn build:patterns to see the parsers still process the patterns
3. Run yarn test:php to run the unit tests

[adamwoodnz]

🎉 LGTM

Thanks so much for working on this, and cleaning up the Swag page, oops!

Tested as instructed, also checked patterns loaded locally. Not exactly sure what changed in History, but page looks correct 🤷‍♂️

[ryelle]

Not exactly sure what changed in History, but page looks correct

Yeah, my local git client showed the exact change better, it's this:

- <td>No <?php _e( 'Musician', 'wporg' ); ?> chosen.</td>
+ <td><?php _e( 'No musician chosen.', 'wporg' ); ?></td>

Not sure why the parser only pulled out "Musician" in the first place 🤷🏻