wit-component, wit-parser: preserve doc comments through embed path

[Mees-Molenaar]

For our use case, we want to store some metadata in comments in the wit file. According to the documentation, this should be available. However, we encountered that the embedding path (which is used by wit-bindgen) did not include the comments. This PR fixes that.

[alexcrichton]

Thanks! Given the test failures I think it might make sense to ignore errors when decoding this section rather than propagating them up? That looks to be masking other errors and/or causing minor issues.

[Mees-Molenaar]

Thanks for quick review, I agree with your comment.
I have adjusted it, is this what you had in mind?

I only see that an offset is now not matching because of an offset. Is that something I need to commit, or do I need to change the implementation so that the offset keeps the same?

[alexcrichton]

Oh offsets changing is fine, that's because there's more stuff in the wasm module now the docs). You can fix that by running the test suite with BLESS=1 for that. Also, could you add some comments for why the errors are ignored here?