Run prompt_acceptance_callback on API prompt closed

Runs the prompt_acceptance_callback in the
SaveAutofillPredictionImprovementsController to notify the binder
(UserAnnotationsService) about the user decision (prompt accepted or
not).

ChromeAutofillClient (only failed code coverage check).

Low-Coverage-Reason: TRIVIAL_CHANGE - trivial change in
Fixed: 366183828,365910728
Change-Id: I42921844c33bf64852358a7574259d90c4f936b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5854870
Reviewed-by: Bruno Braga <brunobraga@google.com>
Commit-Queue: Wolfgang Billenstein <bwolfgang@google.com>
Cr-Commit-Position: refs/heads/main@{#1356460}