jaxlib: Expose the status attributes on XlaRuntimeError.
The exception message is unchanged, as verified by a battery of existing unit
tests.
The actual absl::Status itself can't be exposed because the type caster would
turn it into another exception, but we can expose the code/message and a simple
string form that matches the current setup.
Any XlaRuntimeError that doesn't have a Status will report UNKNOWN and the
string passed to it, as that seems like an easier default than propagating the
optional nature.
XLA isn't making compatibility guarantees at this point on the contents of
these attributes, so code that looks at them may need to be updated over time,
but that's no different (and less hacky) than checking e.args[0] for the string
message.
PiperOrigin-RevId: 881546012
