Adds the `wp_set_script_translations()` function which registers translations for a JavaScript file. This function takes a handle, domain and optionally a path and ensures JavaScript translation files are loaded if they exist.
Merges [43825,43828,43859,43898] from the 5.0 branch to trunk.
Props herregroen, atimmer, omarreiss, nerrad, swissspidy, ocean90, georgestephanis.
Fixes#45103, #45256.
git-svn-id: https://develop.svn.wordpress.org/trunk@44169 602fd350-edb4-49c9-b593-d223f7449a82
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