feat(menu): allow showing virtual text below entries

[willothy]

This PR adds the ability to show virt_text below each menu entry:

2023-09-25.06-10-53.mp4

[Bekaboo]

@willothy Thanks but the videos seems to be a demo of overseer.nvim instead of this plugin? Sorry I don't get the point of this PR, could you explain it further?

[willothy]

The demo is of the custom ui.select menu I made based on the dropbar menu. This PR adds the ability for each menu entry to (optionally) display a line of virtual text below it. This can be useful for providing extra info for each entry without extending the lines, and since it's virtual text the cursor will skip over it and still only highlight each entry.

The virtual text in the demo is the explanations of each command - you can see it is highlighted as Comment and is skipped over by the cursor.

By default this PR does nothing to change the winbar or dropdown menus, but it provides the virt text as an extension to the current API so that it can be used when creating other kinds of menus.

[Bekaboo]

Could we use Pascal case for the virtualtext namespace?

[willothy]

Updated branch and changed the namespace id :)

[willothy]

Awesome! Is the ui-select menu something you'd want to integrate into the plugin, or should I just keep that for my own config?

[Bekaboo]

@willothy It would be greate if you can help integrating ui-select into this plugin :D

[willothy]

@willothy It would be greate if you can help integrating ui-select into this plugin :D

Sounds good! My current implementation works but contains a few hacky things for my config, I'll clean it up and open a PR :)