feat: add highlight provider

[pinbraerts]

Reused code from vim.show_pos. Tried to override vim.api.nvim_echo, but it is extremely unsafe and messed up gui a bit. Then I tried to capture output of the command into buffer but that droped highlights.

I use vim.o.cmdheight = 0 and status bar blinks. Looks like something is blocking gui. Leaving it as draft until I figure out why.