Convert frontend code to typescript (#31559)

None of the frontend js/ts files was touched besides these two commands
(edit: no longer true, I touched one file in
61105d0618
because of a deprecation that was not showing before the rename).

`tsc` currently reports 778 errors, so I have disabled it in CI as
planned.

Everything appears to work fine.

web_src/js/standalone/swagger.ts

@@ -0,0 +1,32 @@
+import SwaggerUI from 'swagger-ui-dist/swagger-ui-es-bundle.js';
+import 'swagger-ui-dist/swagger-ui.css';
+
+window.addEventListener('load', async () => {
+  const url = document.querySelector('#swagger-ui').getAttribute('data-source');
+  const res = await fetch(url);
+  const spec = await res.json();
+
+  // Make the page's protocol be at the top of the schemes list
+  const proto = window.location.protocol.slice(0, -1);
+  spec.schemes.sort((a, b) => {
+    if (a === proto) return -1;
+    if (b === proto) return 1;
+    return 0;
+  });
+
+  const ui = SwaggerUI({
+    spec,
+    dom_id: '#swagger-ui',
+    deepLinking: true,
+    docExpansion: 'none',
+    defaultModelRendering: 'model', // don't show examples by default, because they may be incomplete
+    presets: [
+      SwaggerUI.presets.apis,
+    ],
+    plugins: [
+      SwaggerUI.plugins.DownloadUrl,
+    ],
+  });
+
+  window.ui = ui;
+});