Detection of support for custom formatters doesn't work

Hi,

The mechanism used to detect support for custom formatters doesn't work. It will always report that custom formatters are not supported or that support is disabled. This is due to the fact that the detection mechanism relies on the application of a custom formatter when strings are logged to the console. However, custom formatters are not applied when logging strings. They are only applied when logging objects.

Executing the following statements in the console will demonstrate this:

```
window.devtoolsFormatters = [{"header": () => {console.count("formatter"); return null;}}]
console.log("string")
console.log({})
```

You'll see that the counter "formatter" is only increased once, when the last statement is executed. I see the same behavior using both Chrome and Firefox.