feat: better preview with the heading line at the top of the window about telescope-heading.nvim HOT 2 OPEN

@sankantsu Thanks for your great explanation.
Generally, I like the idea. But telescope-heading is a telescope picker not previewer yet. Is it better if we made it a standalone previewer extension or even push into telescope core?

from telescope-heading.nvim.

I think it is convinient if the telescope.nvims builtin vim_buffer_vimgrep previewer itself supports this type of customization. But currently it seems that telescope.nvim team generally do not want addition or feature enhancement of builtin picker/previewers to avoid extra maintainance costs. So I think providing previewer as an extension would be better.
nvim-telescope/telescope.nvim#1228

The above previewer is actually (a little) improved version of what I wrote in this issue.
nvim-telescope/telescope.nvim#2786

I implemented this previewer basically only for this telescope-heading.nvim picker. So it seems natural to me that the specialized previewer would be bundled with the picker.
But if you like separate repository for the previewer, it also makes sense.

from telescope-heading.nvim.