I18N: Introduce `load_script_translations()` as a wrapper for loading and...

I18N: Introduce `load_script_translations()` as a wrapper for loading and filtering translation data for JavaScript files.

* Introduces `pre_load_script_translations` to short-circuit the function.
* Introduces `load_script_translation_file` to filter the file path for loading script translations.
* Introduces `load_script_translations` to filter the JSON-encoded translation data.

Props johnbillion, strategio, swissspidy, dimadin, ocean90.
Merges [44232] to trunk.
Fixes #45425.
Built from https://develop.svn.wordpress.org/trunk@44316


git-svn-id: https://core.svn.wordpress.org/trunk@44146 1a063a9b-81f0-0310-95a4-ce76da25c4cd