Support visibility change notifications in AutofillProvider.java.

Android API level 27 (released December 2017) added support for
communicating visibility changes in forms during an ongoing Android
Autofill session.

This CL is the first in a series to add support for visibility changes
in WebView. It adds the required wiring between AutofillProvider.java
and the Android framework classes. It also adds setters and getters
for the visibility attribute of FormFields.

Low-Coverage-Reason: Pure wrapper class & more tests to be added later.
Bug: 1482048
Change-Id: Id2022cf498c808be487ac07fc9450672e65c07c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4863243
Reviewed-by: Dominic Battre <battre@chromium.org>
Commit-Queue: Jan Keitel <jkeitel@google.com>
Cr-Commit-Position: refs/heads/main@{#1197603}