fix(v2): Add all webpack module aliases to type declaration file (#2687)

packages/docusaurus-module-type-aliases/src/index.d.ts

@@ -41,3 +41,15 @@ declare module '@theme/*' {
   const component: any;
   export default component;
 }
+
+declare module '@docusaurus/*';
+
+declare module '*.module.css' {
+  const classes: {readonly [key: string]: string};
+  export default classes;
+}
+
+declare module '*.css' {
+  const src: string;
+  export default src;
+}