Consolidate BWU service ID bookkeeping into the BaseBwuHandler class. This eliminates duplicated code in per-medium BWU handlers and allows us to easily augment the bookkeeping with endpoint IDs in a subsequent CL.
Also, localize all service ID wrapping to the BaseBwuHandler class. A postfix is appended to the service ID during bandwidth upgrade, e.g., "NearbyShare_INITIATOR_BWU"; this is done to distinguish a medium's use for advertising/discovery vs. its use for device-to-device connections.
This CL should theoretically be a no-op, but per-medium BWU handlers were inconsistent in their implementations.
PiperOrigin-RevId: 442019603
Edwin Wu