Recreate identity if private key loading fails

It seems like secureenclave keys can disappear from the keychain in,
e.g., some backup and restore scenarios. This new logic will overwrite
an old identity with a new one anytime the key loading fails (regardless
of whether it was not found or some other issue). The current hypothesis
is that the vast majority of these errors will be due to the key no
longer existing on the device. Other metrics were landed to verify that
hypothesis but, for now, this current change will attempt to overwrite
all problematic keys.

Bug: 414659932
Change-Id: I479ff24f8e830869204deb9fc8a2c975435be45d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6519873
Reviewed-by: Hamda Mare <hmare@google.com>
Commit-Queue: Sébastien Lalancette <seblalancette@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1457101}