Add WebAssembly/TypeScript bindings (#5762)

* Add TypeScript bindings

* mark Z3_eval_smtlib2_string as async

src/api/js/src/async-wrapper.js

@@ -0,0 +1,38 @@
+// this wrapper works with async-fns to provide promise-based off-thread versions of some functions
+
+let capability = null;
+function resolve_async(val) {
+  // setTimeout is a workaround for https://github.com/emscripten-core/emscripten/issues/15900
+  if (capability == null) {
+    return;
+  }
+  let cap = capability;
+  capability = null;
+
+  setTimeout(() => {
+    cap.resolve(val);
+  }, 0);
+}
+
+function reject_async(val) {
+  if (capability == null) {
+    return;
+  }
+  let cap = capability;
+  capability = null;
+
+  setTimeout(() => {
+    cap.reject(val);
+  }, 0);
+}
+
+Module.async_call = function (f, ...args) {
+  if (capability !== null) {
+    throw new Error(`you can't execute multiple async functions at the same time; let the previous one finish first`);
+  }
+  let promise = new Promise((resolve, reject) => {
+    capability = { resolve, reject };
+  });
+  f(...args);
+  return promise;
+};