BridgeJS: support imports of JS Promise as async Swift

[MaxDesiatov]

Supersedes #486.

Provides a motivating example with fetchWeatherData() test. The full end-to-end flow works:

1. TypeScript interface WeatherData { temperature: number; description: string; humidity: number; };
2. Function fetchWeatherData(city: string): Promise<WeatherData>;
3. JS returns Promise.resolve({ temperature: 15.5, description: "Cloudy", humidity: 80 });
4. Swift awaits and gets a typed WeatherData struct with .temperature, .description, .humidity properties;
5. No Foundation, no Codable, no manual JSValue unwrapping for this and analogous functions backed by fetch(...).json().

Compatible with Embedded Swift.

Additionally, @JSFunction now supports async effects.

[kateinoigakukun]

I think we need a different approach using JSTypedClosure to avoid the boxing

[kateinoigakukun]

Can you follow the pattern we have in recent other suites like https://github.com/swiftwasm/JavaScriptKit/blob/main/Tests/BridgeJSRuntimeTests/ArraySupportTests.swift ?

[MaxDesiatov]

Can you elaborate? Which specific pattern are you referring to? I suppose that's not the use of XCTest?

[kateinoigakukun]

I mean, I'd like to avoid adding more and more imports in prelude.mjs and want to split into separate file like this: https://github.com/swiftwasm/JavaScriptKit/blob/main/Tests/BridgeJSRuntimeTests/JavaScript/ArraySupportTests.mjs

[MaxDesiatov]

Thanks, also addressed