[iOS cont. panel] Added IPH FET impression tracking per-infoblock

The infoblocks now pass their FET feature, as well as that feature's
"used" event string, to the entrypoint through the config so that they
can control the amount of impressions of the IPH. The entrypoint also
fires the "used" event whenever the entrypoint is tapped with that
infoblock's config active.

difficult to unit test, will be adding EG tests separately.

Low-Coverage-Reason: TESTS_IN_SEPARATE_CL browser_coordinator is
Bug: b:335470692
Change-Id: I4d19d5e2c630ae61b135c700a4b5186251395ede
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5626822
Reviewed-by: Robbie Gibson <rkgibson@google.com>
Commit-Queue: Nicolas MacBeth <nicolasmacbeth@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1322767}