Add Inline color span

[BlueWhaleYT]

It would be good if there is an inline color span next to the color code e.g. hex, rgb.
With this, we can instantly know what the color is.

Like VSCode, a tiny color block is embed at the start of the color code.

[dingyi222666]

It's hard to implement.
For this to work, the inlay hint has to be implemented first.

[Rosemoe]

Actually it's a sub feature of inlay hints.
See also #341