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/htmx.ts

@@ -0,0 +1,20 @@
+import {showErrorToast} from './modules/toast.ts';
+
+// https://github.com/bigskysoftware/idiomorph#htmx
+import 'idiomorph/dist/idiomorph-ext.js';
+
+// https://htmx.org/reference/#config
+htmx.config.requestClass = 'is-loading';
+htmx.config.scrollIntoViewOnBoost = false;
+
+// https://htmx.org/events/#htmx:sendError
+document.body.addEventListener('htmx:sendError', (event) => {
+  // TODO: add translations
+  showErrorToast(`Network error when calling ${event.detail.requestConfig.path}`);
+});
+
+// https://htmx.org/events/#htmx:responseError
+document.body.addEventListener('htmx:responseError', (event) => {
+  // TODO: add translations
+  showErrorToast(`Error ${event.detail.xhr.status} when calling ${event.detail.requestConfig.path}`);
+});