Fix a number of typescript issues (#32308)

- Prefer
[window.location.assign](https://developer.mozilla.org/en-US/docs/Web/API/Location/assign)
over assigning to
[window.location](https://developer.mozilla.org/en-US/docs/Web/API/Window/location)
which typescript does not like. This works in all browsers including
PaleMoon.
- Fix all typescript issues in `web_src/js/webcomponents`, no behaviour
changes.
- ~~Workaround bug in `@typescript-eslint/no-unnecessary-type-assertion`
rule.~~
- Omit vendored file from type checks.
- `tsc` error count is reduce by 53 with these changes.

web_src/js/webcomponents/absolute-date.ts

@@ -26,7 +26,7 @@ window.customElements.define('absolute-date', class extends HTMLElement {
     this.shadowRoot.textContent = toAbsoluteLocaleDate(this.getAttribute('date'), lang, opt);
   };
 
-  attributeChangedCallback(_name, oldValue, newValue) {
+  attributeChangedCallback(_name: string, oldValue: string | null, newValue: string | null) {
     if (!this.initialized || oldValue === newValue) return;
     this.update();
   }