[Data Sharing] Integration for showing create and join flows preview image.

In this CL,
- Adding utility method to convert SavedTabGroup tabs to TabPreview.
- Fetching favicons from urls for all tabs.
- Using RuntimeData to set PreviewData for create and join flows.

Bug: 380891795
Change-Id: I0ffb55b9e614153a6e5183a72747b7ed1d1fb1c3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6108320
Reviewed-by: Siddhartha S <ssid@chromium.org>
Commit-Queue: Ritika Gupta <ritikagup@google.com>
Auto-Submit: Ritika Gupta <ritikagup@google.com>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1399390}