Disable app_function service on Wear

This change introduces a configuration class, which allows for
customization of when the AppFunctionManager is available. At the
moment, we're using this to remove support for it on Wear, which
does not have an immediate use-case for the service.

Bug: 361300136
Test: Local boot testing on Wear
Flag: android.app.appfunctions.flags.enable_app_function_manager
Change-Id: Ia0e1e355999c5bb724f6f94cb17eafd169214abe