WP-scripts: Add command to create Jed-compatible JSON files

[Paulsky]

I would like a command to generate json files from po files in my language directory. For example: wp-scripts i18n-make-json.

This function was added in wp-cli: wp-cli/i18n-command#108

I'm not using the wp-cli in my current project. If I would like to generate Jed-compatible JSON files, I have to setup wp-cli only for this purpose, or install some (outdated) npm package like po2json (which only takes single files, not directories, and doesn't generate the recommanded file names:

• <text domain>-<locale>-<script handle>.json
• <text domain>-<locale>- md5hashoftherelativepathofthefile.json

See: https://developer.wordpress.org/block-editor/how-to-guides/internationalization/#load-translation-file

By the way, I think people (including myself) finding this way of setting the script translations really confusting, cumbersome, buggy: https://wordpress.stackexchange.com/questions/407346/using-wp-set-script-translations-without-manually-registering-the-script

I have 3 locales and 2 script entry points. So I have to make:

• <text domain>-<locale1>- handle1.json
• <text domain>-<locale2>- handle1.json
• <text domain>-<locale3>- handle1.json
• <text domain>-<locale1>- handle2.json
• <text domain>-<locale2>- handle2.json
• <text domain>-<locale3>- handle2.json