disambiguate wasi by renaming it to wasip1

[codefromthecrypt]

Comments happened on #964 (comment) post merge, about how "wasi" is ambiguous, and Go disambiguated it with "wasip1". As the issue was already merged, comments didn't really lead to action.

Since then, rust and JS are beginning to enforce a wasi version similar, if not exactly the same as the Go discussion. I think we shouldn't really keep "wasi" knowing this, especially as the whole thing is new might as well do it right.

My suggestion is to keep the short name go uses "wasip1" as we know it is incompatible with subsequent versions. Without this, runtimes can't use the OS to figure out if the code might run or not, invalidating the concept entirely.