Themes: Support title in templateParts

[Mamaduka]

Description

Adds "title" support in templateParts theme.json configuration.

Fixes #34723.

Cc @gziolo, I saw that you introduced i18n for the customTemplates title, and I just wanted to check if I'm handling it correctly here.

How has this been tested?

1. Update templateParts definition in theme, e.g. Blockbase.
2. Go to the Site Editor -> Template Parts.
3. Check that provided "title" is displayed.

Example

"templateParts": [
      {
	      "name": "header",
	      "title": "Header",
	      "area": "header"
      },
      {
	      "name": "footer",
	      "title": "Footer",
	      "area": "footer"
      }
]

Screenshots

Before	After

Types of changes

Enhancement

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[gziolo]

I saw that you introduced i18n for the customTemplates title, and I just wanted to check if I'm handling it correctly here.

It should work on the Gutenberg/WordPress core side, but we also will have to open a patch against WP-CLI to update the i18n schema used there.

Edit: it looks like it should be automated now:

https://github.com/wp-cli/i18n-command/blob/ea8a6b3ab19c490798b420beabf06ece40b8e708/src/ThemeJsonExtractor.php#L19

[Mamaduka]

it looks like it should be automated now:

Great news. Thanks, @gziolo.

[gziolo]

There is another unit test that covers translations in theme.json that could get updated, too:
https://github.com/WordPress/gutenberg/blob/trunk/phpunit/class-wp-theme-json-resolver-test.php#L191-L199

[Mamaduka]

@gziolo, how do you update language files for the test theme?

[Mamaduka]

@gziolo figured it out.

P.S. Sorry about my Polish; I had to use a google translator.

[gziolo]

@gziolo figured it out.

P.S. Sorry about my Polish; I had to use a google translator.

Good job updating the test 👍

I guess the translation is correct 😃

[gziolo]

It looks good and it has enough test coverage 🚀