investigate whether date and time <input> types leak the user's locale

The date and time types were enabled during the ESR60 development cycle. We should verify that these features do not leak the user's locale, e.g., are the input field dimensions different in different locales? See: ​ https://bugzilla.mozilla.org/show_bug.cgi?id=1399036

If necessary, we can set the dom.forms.datetime pref to false to remove support for these types.