BridgeJS: Support `@JS struct` on return type of async exported `@JS func`

[kateinoigakukun]

https://swiftwasm.org/JavaScriptKit/PlayBridgeJS/?code=H4sIAAAAAAAAE6tWKi7PTCtRslJy8ApWKC4pKk0uUXDLz1eoro3JAwmlleYlK6Snlrjl52toKiQWV%2BYlK%2BjaQZUo6SillBQrWSkp1QIAGbFRnEkAAAA%3D&enc=gzip-b64

Input:

@JS struct Foo {}
@JS func getFoo() async -> Foo {}

Expected Output:

@JSFunction func Promise_resolve_<mangled Foo>(_ promise: JSObject, _ value: Foo) throws(JSException)
@JSFunction func Promise_reject(_ promise: JSObject, _ value: JSValue) throws(JSException)

@_expose(wasm, "bjs_getFoo")
@_cdecl("bjs_getFoo")
public func _bjs_getFoo() -> Int32 {
 #if arch(wasm32)
 return _bjs_makePromise(resolve: Promise_resolve_<mangled Foo> reject: Promise_reject) {
 return await getFoo()
 }
 #else
 fatalError("Only available on WebAssembly")
 #endif
}

Actual Output:

@_expose(wasm, "bjs_getFoo")
@_cdecl("bjs_getFoo")
public func _bjs_getFoo() -> Int32 {
 #if arch(wasm32)
 let ret = JSPromise.async {
 return await getFoo().jsValue
 }.jsObject
 return ret.bridgeJSLowerReturn()
 #else
 fatalError("Only available on WebAssembly")
 #endif
}

[krodak]

#758 closed