[Tab Group Sync] Transition from saved to shared tab group

This CL fixes the transition from saved to shared tab group when shared
from UI. It does not cover the transition on remote devices.

Prior to this CL local tab IDs were moved in the model directly without
proper updates of observers. This CL uses standard methods like connect
and disconnect saved groups with or from tab group in UI.

MakeTabGroupShared() method is removed from the model because it does
not contain any additional logic and can be implemented using Add()
method.

Note that the originating saved tab group should eventually be removed
from the model but without issuing tombstones to the server. This is
not covered by this CL and will be done once the transition is fully
implemented.

Shared tab group data integration test moved to desktop-only because
it requires using Browser which is not available on Android.

Bug: 370745855
Change-Id: Ib7fbe7fa56f4129b9eb6018946a174592cbf318b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5956815
Commit-Queue: Rushan Suleymanov <rushans@google.com>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Darryl James <dljames@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1375714}