libbinder: support calls over sockets

Minimal-ish change for basic binder RPC.

This enables binder to work over sockets. The main change to core code
is in 'Parcel' and 'BpBinder'. The Parcel format is now associated with
the binder that it is either for or a reply from (we no longer have
binder 'objects' for the kernel). BpBinder is extended to support
talking over sockets (ideally, this would be a subclass, but
IBinder::localBinder/remoteBinder mean there is a lot of code which
presupposes what type of binder we have).

In addition, we have a few new objects:
- RpcServer - set this up to serve a connection
- RpcConnection - symmetrical object handling dispatch to a known
    server/client
- RpcAddress - (this will definitely change) randomly generated
    addresses - this might include things like host VM context, ip
    address, or similar in the future. In that case, the address
    generation should be cryptographically secure.
- RpcState - this keeps track of known binders, their refcounts, and
    async transactions, and it understand the binder socket wire
    protocol

The connection itself looks like N socket accepts to a server (the
server might have M socket accepts back to the client for symmetrical
connections, that is connections which need more than nested
transactions). The number of these socket connections controls how many
synchronous transactions can be made. Wherever possible, the behavior
here seeks to mimick the binder driver, and some differences are
documented in the code.

After this CL merges, the future work I intend on completing includes:
- support to work over vsock
- performance benchmarking
- optimization of the socket code here (may include delaying refcounts)
- support to pass 'transitive' binders (pass a binder from one service
  to a different service, to let it setup a new connection). This task
  may be excluded from my efforts as a security hedge if I can manage.
- fuzzer for this wire format
- support for linkToDeath
- support for transaction encryption
- support for promoting from a weak pointer
- handling SIGPIPE for dead connections
- and many more! :)

Bug: 167966510
Test: binderRpcTest

Change-Id: I276c6e312f584b57f4e7a14389ea4a1d63cfa2f4