lint: add tsconfig for browser_tests, fix existing violations (#5633)

## Summary

See https://typescript-eslint.io/blog/project-service/ for context.
Creates a browser_tests specific tsconfig so that they can be linted.

Does not add a package.json script to do the linting yet, but `pnpm exec
eslint browser_tests` should work for now.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5633-lint-add-tsconfig-for-browser_tests-fix-existing-violations-2726d73d3650819d8ef2c4b0abc31e14)
by [Unito](https://www.unito.io)

browser_tests/fixtures/ws.ts

@@ -12,9 +12,10 @@ export const webSocketFixture = base.extend<{
           // so we can look it up to trigger messages
           const store: Record<string, WebSocket> = ((window as any).__ws__ = {})
           window.WebSocket = class extends window.WebSocket {
-            constructor() {
-              // @ts-expect-error
-              super(...arguments)
+            constructor(
+              ...rest: ConstructorParameters<typeof window.WebSocket>
+            ) {
+              super(...rest)
               store[this.url] = this
             }
           }