[1/N][Requesting Handoff from App] Create HandoffActivityDataSerializer

This is part of a stack of changes to send requests for Handoff to connected associations and process response messages into actual app launches

Create a class capable of reading and writing HandoffActivityData objects from proto streams

Test: Added unit tests
Bug: 400970610
Flag: android.companion.enable_task_continuity
Change-Id: I350a63755bbe416f2f6b04c63ffc285420c79ece