Ability to create virtual spaces (indentation)

[IllustratedMan-code]

Feature already in Vim?

no

Feature description

Add ability to set extmarks at the beginning of a line while offsetting existing text. Something like:

vim.api.nvim_buf_set_extmark(0, 1, 0, 0, {virt_text = {{"  ", "none"}}, virt_lines_pos="bol"})

would change this:

** my heading
other text

to this:

  ** my heading
other text

This would make implementing things like org-indent-mode possible.

[clason]

Duplicate of #9496