Observes Android content filters from Service.

Creates a JNI component bridge that integrates SupervisedUserService
with observation of Android Secure Settings. That bridge allows creating
a Java class instance as a component of chromium service. That instance
notifies service callbacks when the status of Android settings changes.

The feature is disabled by default, which means that both bridges would
remain inactive code until activated.

Bug: 422091648
Low-Coverage-Reason: EXPERIMENTAL_CODE disabled by default
Change-Id: I5761c50a262c5712da36e1bdf7b6d8e061093447
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6612425
Commit-Queue: Tomek Jurkiewicz <tju@google.com>
Reviewed-by: Boris Sazonov <bsazonov@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1469546}