Add inlay hints

[truelossless]

Add support for the highlight group LspInlayHint. This should fix #44.
I chose arbitrary colors but I think they're quite close to those in the Helix theme.

Before:

After:

After, Mirage :

[Shatur]

I think that inlay hints needs to be grayish. Here is how it looks in VSCode with the same theme with Mirage:

[truelossless]

Alright, I used the comment color instead. Is it better or should I define/reuse another gray tone?

[Shatur]

It looks nicer, but it might worth to use a different color. Otherwise it blends with comments. Example from VSCode:

[truelossless]

So, I went down a rabbit hole and it turns out that the ayu theme doesn't stylize inlay hints. It's the default style defined by VSCode which is applied. Using it give the expected render:

However VSCode uses a semi-transparent color for the background. Here is an alternative render using bg = colors.line for the background:

[Shatur]

Thank you a lot for looking into it! Also thanks for providing screenshots for all options!
In my opinion a separate color looks the best, despite it's not standard 🤔 Using "comment" color or "function" with background looks a bit distracting.

Here is an alternative render using bg = colors.line for the background:

This looks nice, but in my opinion without the background it's a bit better.
What do you think?

We probably better to leave the comment for this new color (that it's taken from VSCode not part actually a part of ayu).

[truelossless]

I agree that without the background it looks less distracting and closer to VSCode, even if I quite like the Helix style. I've added a comment as you suggested!