Allow a module to implement an interface

It would be useful when a module can implement an interface using the implements keyword. Syntax: module MyModule implements MyInterface { ... }.

Example:

interface Showable {
    show(): void;
}
function addShowable(showable: Showable) {

}

// This works:
module Login {
    export function show() {
        document.getElementById('login').style.display = 'block';
    }
}
addShowable(Login);

// This doesn't work (yet?)
module Menu implements Showable {
    export function show() {
        document.getElementById('menu').style.display = 'block';
    }
}
addShowable(Menu);

该 issue 未指出源文件、测试或编译器入口点。首先定位模块声明和接口兼容性的处理逻辑，然后为 module Menu implements Showable 添加覆盖，并确认现有的 addShowable(Menu) 示例可以通过类型检查。