Refactor the credential selection dialog mojo from glic:: to actor::

This allows glic.mojom to depend on actor_webui.mojom. The big benefit
is that we can freely handle the credential selection response in the
actor code space instead of inside glic_page_hander.cc.

There is no behavior change in this CL. The implementation of the IPC is
in the child CL https://crrev.com/c/6867438

bug: b:427817882

Change-Id: If680927abb396229d206004d039a4f7735becb88
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6884892
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Dan Harrington <harringtond@chromium.org>
Commit-Queue: William Liu <liuwilliam@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1506768}