[Android][3PPWM] Disable toggle to prevent using AwG in 3P mode

If AwG is the system autofill provider, Chrome falls back to its own
Autofill mechanism. Therefore, prevent that users toggle the setting if
it can not be effective by disabling the toggle.
For debugging purposes, allow to skip that restriction with a feature
parameter.
The AutofillClientProviderUtils has a test override that resets
automatically.

Screenshot: http://screen/AGe8U7CNCctSqSs.png
Feature Guard: AutofillVirtualViewStructureAndroid
Context: go/3ppwm-dd

Bug: 337003435
Change-Id: Iba093c9fc1b845023fd7ad31acee31be73ffb4e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5490108
Commit-Queue: Friedrich Horschig <fhorschig@chromium.org>
Reviewed-by: Ioana Pandele <ioanap@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1299225}