Add support for NotRestoredReasons above 63 to BFCache tests.

Previously we only supported the enum values up to 63. This is being
done to support https://crrev.com/c/6198936.

This migrates the code to use EnumSet which matches the code in
back_forward_cache_metrics.cc more closely.

Change-Id: I1ba3e8a7e564b03a46cbd623466ffb891d1a694b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6217562
Commit-Queue: Fergal Daly <fergal@chromium.org>
Auto-Submit: Fergal Daly <fergal@chromium.org>
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1414761}