Preserve ESM for async imports to work correctly

babel.config.js

@@ -0,0 +1,26 @@
+module.exports = {
+    sourceMaps: true,
+    presets: [
+        [
+            "@babel/preset-env",
+            {
+                targets: {
+                    esmodules: true,
+                },
+                // We want to output ES modules for the final build (mostly to ensure that
+                // async imports work correctly). However, jest doesn't support ES modules very
+                // well yet (see https://github.com/jestjs/jest/issues/9430), so we use commonjs
+                // when testing.
+                modules: process.env.NODE_ENV === "test" ? "commonjs" : false,
+            },
+        ],
+        "@babel/preset-typescript",
+    ],
+    plugins: [
+        "@babel/plugin-proposal-numeric-separator",
+        "@babel/plugin-proposal-class-properties",
+        "@babel/plugin-proposal-object-rest-spread",
+        "@babel/plugin-syntax-dynamic-import",
+        "@babel/plugin-transform-runtime",
+    ],
+};

src/models/MSC3089TreeSpace.ts

@@ -35,7 +35,7 @@ import { ISendEventResponse } from "../@types/requests";
 import { FileType } from "../http-api";
 import { KnownMembership } from "../@types/membership";
 import { RoomPowerLevelsEventContent, SpaceChildEventContent } from "../@types/state_events";
-import { EncryptedFile, FileContent } from "../@types/media";
+import type { EncryptedFile, FileContent } from "../@types/media";
 
 /**
  * The recommended defaults for a tree space's power levels. Note that this