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/modules/fomantic/base.ts

@@ -0,0 +1,18 @@
+let ariaIdCounter = 0;
+
+export function generateAriaId() {
+  return `_aria_auto_id_${ariaIdCounter++}`;
+}
+
+export function linkLabelAndInput(label, input) {
+  const labelFor = label.getAttribute('for');
+  const inputId = input.getAttribute('id');
+
+  if (inputId && !labelFor) { // missing "for"
+    label.setAttribute('for', inputId);
+  } else if (!inputId && !labelFor) { // missing both "id" and "for"
+    const id = generateAriaId();
+    input.setAttribute('id', id);
+    label.setAttribute('for', id);
+  }
+}