Expose the open by default settings screen to apps

With the changes for app links v2, apps need a way to link users into
the domain selection screen if the app relies on opening web links
for some functionality.

To achieve that, this exposes the existing action,
ACTION_APP_OPEN_BY_DEFAULT_SETTINGS, from android.provider.Settings
and removes the permission needed to launch the relevant Activity,
since it's no longer required.

Note that this will also require a change to remove the enforcement
from the Activity declaration, which will be a follow up.

Bug: 178648367

Test: none, unhide API

Change-Id: I73231b9b4686ee67490ffe1526542b2f59c8089b