Clean up get_plugin_data() and _get_plugin_data_markup_translate(), and...

Clean up get_plugin_data() and _get_plugin_data_markup_translate(), and standardize sanitization. fixes #20266.

git-svn-id: https://core.svn.wordpress.org/trunk@20229 1a063a9b-81f0-0310-95a4-ce76da25c4cd