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/features/repo-issue.ts

@@ -97,7 +97,7 @@ function excludeLabel(item) {
   const regStr = `labels=((?:-?[0-9]+%2c)*)(${id})((?:%2c-?[0-9]+)*)&`;
   const newStr = 'labels=$1-$2$3&';
 
-  window.location = href.replace(new RegExp(regStr), newStr);
+  window.location.assign(href.replace(new RegExp(regStr), newStr));
 }
 
 export function initRepoIssueSidebarList() {