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/origin-url.test.ts

@@ -1,9 +1,9 @@
 import {toOriginUrl} from './origin-url.ts';
 
 test('toOriginUrl', () => {
-  const oldLocation = window.location;
+  const oldLocation = String(window.location);
   for (const origin of ['https://example.com', 'https://example.com:3000']) {
-    window.location = new URL(`${origin}/`);
+    window.location.assign(`${origin}/`);
     expect(toOriginUrl('/')).toEqual(`${origin}/`);
     expect(toOriginUrl('/org/repo.git')).toEqual(`${origin}/org/repo.git`);
     expect(toOriginUrl('https://another.com')).toEqual(`${origin}/`);
@@ -13,5 +13,5 @@ test('toOriginUrl', () => {
     expect(toOriginUrl('https://another.com:4000/')).toEqual(`${origin}/`);
     expect(toOriginUrl('https://another.com:4000/org/repo.git')).toEqual(`${origin}/org/repo.git`);
   }
-  window.location = oldLocation;
+  window.location.assign(oldLocation);
 });