[ORC] Replace the serialize/deserialize function pair with a SerializationTraits

[ORC] Replace the serialize/deserialize function pair with a SerializationTraits
class.

SerializationTraits provides serialize and deserialize methods corresponding to
the earlier functions, but also provides a name for the type. In future, this
name will be used to render function signatures as strings, which will in turn
be used to negotiate and verify API support between RPC clients and servers.

llvm-svn: 281254