Add highlights for nvim-navic

[repl6669]

Hello, I added highlights for nvim-navic.

Before:

After:

Of course feel free to adjust the colors. I tried to pick close matches based on tokyonight config.

[mvllow]

Thank you!

p.green for NavicIconsString isn't in our palette but I'll match up the colours with our syntax anyways :)

[repl6669]

@mvllow Oh, sorry about that p.green, I missed that one. Thank you for merging.