Handle exceptions in AppFunctionManagerServiceImpl

When an exception occurs, the service will return a failure response to the client instead of throwing an exception,

Change-Id: I2aa8d0e22b9edd0334904186dd9bb118f072f4d7
Flag: android.app.appfunctions.flags.enable_app_function_manager
Test: Verified by running locally. Will add CTS in next cl.
Bug: 360864791