JS/TS semantic highlighting for keywords (readonly global vars)


*TS Template added by @mjbvz*

**TypeScript Version**: 4.1.2

**Search Terms**
- semantic highlighting
- constant
- readonly

---

vscode 1.52.0

Code:

```js
undefined;
Infinity;
NaN;
```

Result:

Semantic highlighting recolors `Infinity` and `NaN` from `constant.language` to `variable`.

Expected:

All three identifiers should be colored identically.