Autoloader: use the wp-textdomain npm package to update package textdomains

[kbrown9]

We need to provide a way for a consuming plugin to use its own textdomain in the package strings. This PR presents a possible solution which uses the wp-textdomain NPM package to detect translatable strings and change them to a given textdomain.

How a Consumer Plugin Would Use This

1. Add the jetpack-autoloader package to the plugin's composer dependencies in composer.json. (All plugins that use Jetpack packages should use the autoloader package to load package files.)

2. Add a composer script to the plugins's composer.json file, with the plugin's textdomain as the first argument:
   "post-autoload-dump": "node vendor/automattic/jetpack-autoloader/js/update_textdomain.js {textdomain}"

3. Add wp-textdomain as a development dependency in the plugin's package.json file.

4. When the plugin is built with composer install, composer update or composer dump-autoload, the post autoload dump script will run. The script will update every textdomain in the .php files in the Automattic packages.

Changes proposed in this Pull Request:

• Add wp-textdomain to Jetpack's development dependencies in package.json.

• Add a new file to the autoloader package, update_textdomain.js, which uses wp-textdomain to detect and update the textdomain of package strings.

Why is this in the autoloader package?

I put this in the autoloader package because:

• Every plugin that consumes Jetpack packages should use Jetpack's autoloader.
• This code could (maybe should?) live in its own package, but then consumer plugins will need to include both the autoloader and new textdomain packages.
• The autoloader is already used to build the plugin's composer package manifest files when a consuming plugin is built. Since the textdomains are changed when the plugin is built, the autoloader package seemed like a natural place to include this code.

Jetpack product discussion

• n/a

Does this pull request change what data or activity we track or use?

• no

Testing instructions:

1. Add the composer script to composer.json. Enter a textdomain that's not jetpack so you can verify that the script worked.
   "post-autoload-dump": "node vendor/automattic/jetpack-autoloader/js/update_textdomain.js {textdomain}"

2. Run composer dump-autoload. The textdomain for the translatable strings in the composer packages should be changed from jetpack to the string used in step 1.

Proposed changelog entry for your changes:

• n/a

[jetpackbot]

Scheduled Jetpack release: January 12, 2021.
Scheduled code freeze: January 4, 2021

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Generated by 🚫 dangerJS against 7f10c5e

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello kbrown9! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer and confirm D54127-code works as expected before merging this PR. Once this PR is merged, please commit the changes to WP.com. Thank you!
This revision will be updated with each commit to this PR

[kbrown9]

I'm closing this in favor of PR #18070, which will update the package documentation to provide information about updating textdomains. We've decided that the consumer plugins should implement the tools and processes that fit their needs.