refactor(core): type EMPTY_OBJ as never for improved type safety (a…

…ngular#53571)

Consider a snippet like:

```
const x = directiveDef.inputs || EMPTY_OBJ
```

this currently results in `x` being inferred as just `{}`- ending up
turning of potential future assignment checks. This surfaced in the
`DirectiveDefinition` -> `DirectiveDef` conversion.

Note: This has the effect that assigning `EMPTY_OBJ` to a field of
anything would _always_ pass. It's questionable if this rather impacts
type-safety in a more negative way. There seem to be trade-offs in both
ways... Maybe worth considering just using `{}` directly as fallbacks in
some places, and treating this as an unique symbol?!

https://www.typescriptlang.org/play?#code/MYewdgzgLgBAHgLhmApgNxQJxgXhgbwF8YBDCZdLAbgCgbRJYAHJfGmDmAGxC6SkwBXFABoahAD6CwAExQAzAJaoZuZIK5dS5EmACeteuGgxBapjAkT4VIA

PR Close angular#53571

packages/core/src/util/empty.ts

@@ -14,7 +14,7 @@ import {initNgDevMode} from './ng_dev_mode';
  * code.
  */
 
-export const EMPTY_OBJ: {} = {};
+export const EMPTY_OBJ: never = {} as never;
 export const EMPTY_ARRAY: any[] = [];
 
 // freezing the values prevents any code from accidentally inserting new values in