Add a raw_module attribute to #[wasm_bindgen]

This allows subverting the checks and resolution performed by the
`module` attribute added as part of [RFC 6] and has been discussed in #1343.

Closes #1343

[RFC 6]: https://github.com/rustwasm/rfcs/pull/6

crates/backend/src/encode.rs

@@ -208,6 +208,7 @@ fn shared_import<'a>(i: &'a ast::Import, intern: &'a Interner) -> Result<Import<
             ast::ImportModule::Named(m, span) => {
                 ImportModule::Named(intern.resolve_import_module(m, *span)?)
             }
+            ast::ImportModule::RawNamed(m, _span) => ImportModule::RawNamed(intern.intern_str(m)),
             ast::ImportModule::Inline(idx, _) => ImportModule::Inline(*idx as u32),
             ast::ImportModule::None => ImportModule::None,
         },