lib: add wasm subsystem

[guybedford]

It would be useful to have a generic Web Assembly dedicated subsystem at this point, which also will allow us to handle WASI as well until we have its builtin name set.

[codecov]

Codecov Report

Merging #82 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #82   +/-   ##
=======================================
  Coverage   60.93%   60.93%           
=======================================
  Files          18       18           
  Lines         448      448           
=======================================
  Hits          273      273           
  Misses        175      175

Impacted Files	Coverage Δ
lib/rules/subsystem.js	100% <ø> (ø)	⬆️

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[richardlau]

There's some support for adding wasi instead (or maybe we could add both if that makes sense?): nodejs/node#30258 (comment)

[guybedford]

@richardlau sure, I've added a wasi one as well. Then, if the subsystem changes in the process of merging that PR we can update this too.