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)

eslint.config.ts

@@ -153,5 +153,14 @@ export default defineConfig([
         }
       ]
     }
+  },
+  {
+    files: ['tests-ui/**/*'],
+    rules: {
+      '@typescript-eslint/consistent-type-imports': [
+        'error',
+        { disallowTypeAnnotations: false }
+      ]
+    }
   }
 ])