[Sync] Implement `HintDegradedRecoverabilityChanged()` and calling it

This CL implements `HintDegradedRecoverabilityChanged()` and calling it
when suspecting the degraded recoverability state changed.

Bug: 1247990
Change-Id: I211d261b5d7cef5a54199636e6543e6379f8a266
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3869669


Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Maksim Moskvitin <mmoskvitin@google.com>
Commit-Queue: Mahmoud Rashad <mmrashad@google.com>
Cr-Commit-Position: refs/heads/main@{#1045870}