Adds support for `styleUrls` definitions in the same way `templateUrl`
definitions are provided; clicking on styleUrl will take a user to the
respective file.
Unifies some code in determining a URL definition. We first check if a
url is a `templateUrl`; if it's not, we check that it's a `styleUrl` or
return no definitions.
PR Close#32464
This is in preparation for more rigorous testing of external templates, since it'll work differently under the new tsserver plugin model.
PR Close#30128