Identify a webstate by its snapshot ID when snapshot is updated

This CL addresses an issue introduced in crrev/c/4396359. In that CL,
snapshots are no longer identified by the web state identifier in
SnapshotGenerator and SnapshotCache, but it was not updated in
TabGridMediator and InactiveTabsMediator.

Fixed: 1448506
Change-Id: I82f87846753814e376294942ec1f6c781b65944f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4604412
Commit-Queue: Louis Romero <lpromero@google.com>
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Auto-Submit: Louis Romero <lpromero@google.com>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1155531}