feature: spec versioning

[t3hmrman]

Motivation

Right now, weedle has no way to indicate/control what version of the spec is being read. This can lead to code that is reliant on older features of WebIDL to parse, but not be usable from downstream consumers that expect a more recent version.

One concrete example is the usage of void as a function return which was removed from the spec (undefined should be used instead).

Proposed Solution

If possible, we should add spec-version-aware handling/parsing.

Alternatives

N/A

Additional Context

wasi-gfx/webidl2wit#42