Allow users to set overrides for MediaElement instances by always passing `_wpmejsSettings` instead of just `_wpmejsSettings.pluginPath`.

Props Otto42 for the initial patch.
Fixes #25243.



git-svn-id: https://develop.svn.wordpress.org/trunk@28370 602fd350-edb4-49c9-b593-d223f7449a82