[Autofill in devtools] Test addresses are used to fill forms.

What this CL does?

1. Uses the test addresses set by devtools inside pdm to fill/preview.
   This is done from the external delegate when accepting or selecting
   suggestions.
2. Cleans up test addresses added from ~AutofillHandler
3. Adds the feature flag to control the rollout.

What comes next?

1. Add a metric to measure test addresses being used
2. Update devtools frontend with a full list of test addresses.

Demo: https://screencast.googleplex.com/cast/NDYzMzI5NjU1MzExNTY0OHwwNDlhZWY2ZS05Zg

Bug: 40270486
Change-Id: I4dc1c0ccdf8d4ae2586f767e9275f67f163ee5b5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5400676


Reviewed-by: Danil Somsikov <dsv@chromium.org>
Commit-Queue: Bruno Braga <brunobraga@google.com>
Reviewed-by: Christoph Schwering <schwering@google.com>
Cr-Commit-Position: refs/heads/main@{#1281140}