[iOS][Sync] Add infobar impression histogram split by trigger logic

This CL extends existing Sync.SyncErrorInfobarDisplayed2 histogram by a
adding a suffix split by triggering logic (either because of opening a
new tab or loading a page with a password form).

The total count (by any trigger) is still logged (empty suffix).

Bug: 408165259
Change-Id: Ic7d60d2e967823559a3115d98b439f94ee1b7046
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6526046
Commit-Queue: Rafał Godlewski <rgod@google.com>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Rushan Suleymanov <rushans@google.com>
Cr-Commit-Position: refs/heads/main@{#1458733}