fix evanw#2388: allow consuming types without dom types

Currently the TypeScript types for esbuild depend on the DOM types.
However, esbuild itself does not depend on the DOM.

This change uses type augmentation to make the type error go away, while
keeping backwards support for use with the DOM types.

Closes evanw#2388

lib/shared/types.ts

@@ -635,6 +635,12 @@ export declare function analyzeMetafileSync(metafile: Metafile | string, options
  */
 export declare function initialize(options: InitializeOptions): Promise<void>
 
+declare global {
+  namespace WebAssembly {
+    interface Module {}
+  }
+}
+
 export interface InitializeOptions {
   /**
    * The URL of the "esbuild.wasm" file. This must be provided when running