This fixes an issue where a normal suspending call followed by a plain tail call would result in the tail return value being written to the return pointer of the normal suspending call.
This is fixed by saving the return pointer at the start of the function and restoring it before initiating a plain tail call.
The coroutine lowering pass had issues where it iterated over maps, sometimes resulting in non-deterministic output.
This change removes many of the maps and ensures that the transformations are deterministic.
