Pass arguments via uxn working stack, let callee spill arguments if necessary

[hikari-no-yume]

Currently the caller of a function writes arguments to an in-memory stack (@rbp). If it instead just put them on the uxn working stack and let the callee (the function itself) write them to memory, it would reduce code size when a function is called more than once, and perhaps improve the general readability of the assembly. Maybe we could even use Uxntal's ( a -- b ) syntax for type-checking?

I didn't check if we support struct arguments, but if we do, they would have to be written to memory by the caller still, and then a pointer would be pushed to the uxn working stack.