neovim: Add support for more modes in get_buffer_selection()

[fidgetingbits]

As part of the refactor of get_buffer_selection() we discussed that we don't fully support all modes. The comment was:

  -- FIXME: Resetting the column for CTRL-V seems potentially broken, but
  -- afaik we don't have cursorless tests for this to compare I think?
  -- Note '\22' is '^V' (V-Block)
  -- This is missing some visual modes, but don't know if we care
  -- See: https://github.com/Mbhon1/Osama-Flake/blob/main/terminal/editor/neovim/lua/plugins/lualine/modes.lua

We decided since atm we don't support those in cursorless atm anyway, we will file an issue and remove.

Background discussion was in https://github.com/saidelike/cursorless/pull/9