Ajax: Don't auto-execute scripts unless dataType provided

Ajax: Don't auto-execute scripts unless dataType provided

PR gh-2588 made jQuery stop auto-execute cross-domain scripts unless
`dataType: "script"` was explicitly provided; this change landed in jQuery
3.0.0. This change extends that logic same-domain scripts as well.

After this change, to request a script under a provided URL to be evaluated,
you need to provide `dataType: "script` in `jQuery.ajax` options or to use
`jQuery.getScript`.

Fixes gh-4822
Closes gh-4825
Ref gh-2432
Ref gh-2588