I18N: Fix JavaScript translations for subdirectory installations.

Fixes the `load_script_textdomain` function not resolving the md5 hash based on the relative path for WordPress installations in a subdirectory. Also adds a filter to allow sites using CDNs or other alternative asset locations to filter the relative path resolution.

Props akirk, fierevere, swissspidy, mypacecreator, babaevan, tmatsuur, ocean90, herregroen.

Merges [44209] to trunk.

Fixes #45528.
Built from https://develop.svn.wordpress.org/trunk@44310


git-svn-id: https://core.svn.wordpress.org/trunk@44140 1a063a9b-81f0-0310-95a4-ce76da25c4cd