DO NOT MERGE Allow for HTML styling in mobile data type content descriptions

This CL implements a (somewhat hacky) way to enable HTML attributes in
the mobile data type content description strings. This way we can use
some basic styling in the Quick Settings cellular data tile which uses
it in a TextView.

We do this by assuming that the content description is valid, escaped
HTML, and send two separate CharSequences to all of the listeners, all
of which can then decide if they need the regular content description or
the prettified version.

Test: atest SystemUITests; system ui demo mode
Bug: 141177147
Change-Id: Idf387111b0cdc34ad3762eac0ec6c2b484b393e3