AppFunctionRuntimeMetadata enabled changes

Replacing the AppFunctionRuntimeMetadata.getEnabled() and the
corresponding Builder.setEnabled() signature from a tristate boolean to
an integer.

Flag: android.app.appfunctions.flags.enable_app_function_manager
Test: Pre-existing tests (like setAppFunctionEnabled_functionDefaultEnabled) already test this change.
Bug: 369683073
Change-Id: I6c62e8e4f802d47ee2a648ee334ec44616f3ee0a