Inlay hints look awkward for callback parameters with a single parameter

When you have a callback whose parameter has no parentheses, inlay hints starts to look a little bit weird.

For example, in this code

            return hints.map(hint => ({
                ...hint,
                position: scriptInfo.positionToLineOffset(hint.position),
            }));

you get the following:

Ideally, you'd see that line rewritten as

callbackfn: (hint: InlayHint) => ({
```

Start by reproducing the callback example in the issue and tracing the inlay hints implementation that formats single-parameter arrow callbacks. Compare the current display with the requested callbackfn: (hint: InlayHint) => ( wording. Done means the parameter hint is presented without the awkward layout and existing inlay-hint tests still pass.