[orc-rt] Add transparent SPS conversion for error/expected types. (#161768)
This commit aims to reduce boilerplate by adding transparent conversion
between Error/Expected types and their SPS-serializable counterparts
(SPSSerializableError/SPSSerializableExpected). This allows
SPSWrapperFunction calls and handles to be written in terms of
Error/Expected directly.
This functionality can also be extended to transparently convert between
other types. This may be used in the future to provide conversion
between ExecutorAddr and native pointer types.