[pmo] Use SILBuilder::emitDestructureOperation to destructure values instead of emitting our own tuple_extracts.
This will cause this code to automagically work correctly in ossa code since we
will instead of emitting the tuple_extracts will emit a destructure operation
automagically without code change.
Since this entrypoint will emit tuple_extracts in non-ossa code, this is a NFC
patch.