Introduce SyncableService::StayStoppedAndMaybeClearData for stale data

This adds a new method to allow clearing of any saved account data by a
syncable service. The method is called at most once upon profile load,
if no metadata exists. This helps clearing the account data in the
following cases:
1. If metadata is empty or invalid.
2. If metadata is inconsistent, i.e. metadata exists but initial sync is
   not done. In this case, the metadata is cleared and upon the next
   startup StayStoppedAndMaybeClearData() should be triggered because of
   empty metadata.
3. If metadata is pending to be cleared, for example, if
   ClearMetadataIfStopped() is triggered.

Implementations for this method will come in follow-up CLs.

This CL also introduces a new histogram
Sync.SyncableService.MaybeClearDataIfMetadataEmptyOrInvalid.{type} to
track if the metadata was empty or invalid upon startup and if
StayStoppedAndMaybeClearData() was triggered.

Bug: 401453180
Change-Id: I36e220077409955f4c9e1429fdf8053454cabd30
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6574780
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Rushan Suleymanov <rushans@google.com>
Auto-Submit: Ankush Singh <ankushkush@google.com>
Reviewed-by: Rushan Suleymanov <rushans@google.com>
Cr-Commit-Position: refs/heads/main@{#1470554}