[TabGroupsSync] Cache id mapping to preserve saved state of tab groups

This CL caches the TabGroupId to Saved GUID mapping on browser startup
in order to preserve the saved state of a tab group before the
TabGroupSyncService has initialized.

This prevents duplicate groups from being created when we restart or
crash on startup after the tab group is restored into the browser
but before we connect the tab group to the saved group in
TabGroupSyncService.

Approach:
- On browser startup when RestoreTabGroupMetadata is called cache the
TabGroupId to Saved GUID mapping into SessionService
- When SetTabGroupMetadata is called pull the saved GUID from TGSS if
it's available, otherwise get the id mapping from the cache.
- Write the preserved state to the disk.

Changes:
- Consolidates the retrieval of saved_guid into
SessionService::SetTabGroupMetadata
- Removes the saved_guid parameter from SetTabGroupMetadata since it is
no longer needed
- Adds a mapping for TabGroupId to saved guid string into SessionService
- Updates all callsites of SetTabGroupMetadata to no longer pass in saved_guid
- Removes saved tab group dependency from browser.cc!

Test updated in: chrome/browser/sessions/session_service_unittest.cc

Change-Id: I8a496b2c9992bb525de8aadd1534782e991a0ef5
Bug: 365519965
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5961164
Commit-Queue: Darryl James <dljames@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Eshwar Stalin <estalin@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1375006}