Make fill dialog feature controlled by device config

Use device config to control whether autofill dialog feature is enabled.
To support this, the autofill namespace of DeviceConfig needs to be exposed
for AutofillManager to read in the app thread.
There are augmented_autofill_mode, smart_suggestion_supported_modes and
compat_mode_allowed_packages existed in autofill space. These can be made
app readable.

Bug: 210926084
Test: atest android.autofillservice.cts.dialog.LoginActivityTest
Change-Id: Idfb846656a0c26eba1db4f8ef6ec427ae4ca666d