In #34114, just-in-time (JIT) translation loading was implemented for projects hosted on WordPress.org. This is now expanded to all other plugins/themes.
Projects with a custom `Text Domain` and `Domain Path` header no longer need to call `load_plugin_textdomain()` or `load_theme_textdomain()`.
This reduces the risk of calling them too late, after some translation calls already happened, and generally makes it easier to properly internationalize a plugin or theme.
This moves the `get_plugin_data()` from `wp-admin/includes/plugin.php` to `wp-includes/functions.php` so it's available during the plugin loading process.
Props swissspidy.
Fixes#62244.
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