Generate PHP i18n files in framework

[daledupreez]

We received this report of slowness in the WooCommerce Braintree payment gateway due to the generated translation files still generating only PO and MO files, and not the more performant PHP files that have been in WordPress core since 6.5.

I reviewed the existing GitHub workflow to update translation files in .github/workflows/update-translations-files.yml, but that only generates MO files using the code from the gdcorp-partners/localization-actions. I can't access that upstream repo to see if we could easily add PHP file generation (e.g. by shifting to a more recent version of that upstream code), or if we should aim to use a local script that calls wp i18n make-php from WP-CLI (docs).

[daledupreez]

Also, we probably need to update the SV_WC_Plugin->load_text_domain() function to call only the load_plugin_textdomain() function from WordPress core, rather than forcing a specific .mo file to be loaded.