Add "new conversation" composer for direct messages

ts/util/deconstructLookup.ts

@@ -0,0 +1,21 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { getOwn } from './getOwn';
+import { assert } from './assert';
+
+export const deconstructLookup = <T>(
+  lookup: Record<string, T>,
+  keys: ReadonlyArray<string>
+): Array<T> => {
+  const result: Array<T> = [];
+  keys.forEach((key: string) => {
+    const value = getOwn(lookup, key);
+    if (value) {
+      result.push(value);
+    } else {
+      assert(false, `deconstructLookup: lookup failed for ${key}; dropping`);
+    }
+  });
+  return result;
+};