Clean up npm dependencies (#35484)

- `type-fest` is replaced by our own types
- `@stylistic/eslint-plugin-js` is no longer in use, it was replaced
with `@stylistic/eslint-plugin`
- `@types/license-checker-webpack-plugin` does not apply to our forked
version and has a type stub

web_src/js/modules/observer.ts

@@ -1,5 +1,5 @@
 import {isDocumentFragmentOrElementNode} from '../utils/dom.ts';
-import type {Promisable} from 'type-fest';
+import type {Promisable} from '../types.ts';
 import type {InitPerformanceTracer} from './init.ts';
 
 let globalSelectorObserverInited = false;