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/api.ts

@@ -0,0 +1,40 @@
+import $ from 'jquery';
+
+export function initFomanticApiPatch() {
+  //
+  // Fomantic API module has some very buggy behaviors:
+  //
+  // If encodeParameters=true, it calls `urlEncodedValue` to encode the parameter.
+  // However, `urlEncodedValue` just tries to "guess" whether the parameter is already encoded, by decoding the parameter and encoding it again.
+  //
+  // There are 2 problems:
+  // 1. It may guess wrong, and skip encoding a parameter which looks like encoded.
+  // 2. If the parameter can't be decoded, `decodeURIComponent` will throw an error, and the whole request will fail.
+  //
+  // This patch only fixes the second error behavior at the moment.
+  //
+  const patchKey = '_giteaFomanticApiPatch';
+  const oldApi = $.api;
+  $.api = $.fn.api = function(...args) {
+    const apiCall = oldApi.bind(this);
+    const ret = oldApi.apply(this, args);
+
+    if (typeof args[0] !== 'string') {
+      const internalGet = apiCall('internal', 'get');
+      if (!internalGet.urlEncodedValue[patchKey]) {
+        const oldUrlEncodedValue = internalGet.urlEncodedValue;
+        internalGet.urlEncodedValue = function (value) {
+          try {
+            return oldUrlEncodedValue(value);
+          } catch {
+            // if Fomantic API module's `urlEncodedValue` throws an error, we encode it by ourselves.
+            return encodeURIComponent(value);
+          }
+        };
+        internalGet.urlEncodedValue[patchKey] = true;
+      }
+    }
+    return ret;
+  };
+  $.api.settings = oldApi.settings;
+}