This CL moves the remaining FedCM files in
wpt/credential-management/ to a dedicated FedCM directory.

BUG=347026221

Change-Id: I5509615b793a958061db6ddf8de75a267fe877ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5670976


Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1324607}