update future.{write,read} ABIs

[dicej]

This updates the plumbing, FACT, compilation, and runtime code to use the new ABI defined in WebAssembly/component-model#524.

• future.write now accepts its payload value as up to 4 flat parameters before spilling to linear memory.

• future.read takes no payload pointer when it has no payload type

• {stream,future}.close-{readable,writable} have been renamed to {stream,future}.drop-{readable,writable}

This commit does not address the following items:

• There is no "number of elements written" packed in the high 28 bits of the future.{read,write} results.
• On successful copy, future.{read,write} return COMPLETED instead of CLOSED (which, as noted above, was renamed to DROPPED, making it especially "wrong" as the result code).
• When a future is "done" (by a COMPLETED read/write or by the writable end receiving DROPPED), the only valid operation is future.drop-{readable,writable}. future.{read,write} or lifting traps.
• Because there's no great reason for streams to be more permissive than futures in this regard, streams are also given a "done" state with the same trapping rules as futures, but the stream "done" state is only set when DROPPED is received.

I'll address those in one or more follow-up commits.

[dicej]

Alex, Luke, and I just discussed this and decided we're going to scale back these changes given how big they turned out to be implementation-wise. I'm going to close this and open a new one next week.