[FedCM] Update the title when the RP data changes

In active mode, it is possible that the RelyingPartyData changes
between the loading dialog and the actual accounts chooser.

This CL makes it so that we update the title (and subtitle) whenever
we get a potentially different RelyingPartyData object.

Bug: 442547909
Change-Id: I8b7474f2bac78f33962808645fc6678b6ad08034
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6917354
Reviewed-by: Nicolás Peña <npm@chromium.org>
Commit-Queue: Christian Biesinger <cbiesinger@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1516363}