fix(previewer): preview nvim-jdtls jdt:// entries (closes #728)

Used this opportunity to refactor and simplify the builtin
previewer code.

README.md

@@ -1102,12 +1102,10 @@ require'fzf-lua'.setup {
  -- previewer hidden by default
  winopts = { preview = { hidden = "hidden" } },
  },
- -- uncomment to use the old help previewer which used a
- -- minimized help window to generate the help tag preview
- -- helptags = { previewer = "help_tags" },
- -- uncomment to use `man` command as native fzf previewer
+ -- uncomment to use fzf native previewers
  -- (instead of using a neovim floating window)
  -- manpages = { previewer = "man_native" },
+ -- helptags = { previewer = "help_native" },
  -- 
  -- optional override of file extension icon colors
  -- available colors (terminal):

lua/fzf-lua/defaults.lua

@@ -182,12 +182,8 @@ M.defaults = {
  _ctor = previewers.fzf.man_pages,
  },
  help_tags = {
- split = "botright", -- "topleft"
  _ctor = previewers.builtin.help_tags,
  },
- help_file = {
- _ctor = previewers.builtin.help_file,
- },
  help_native = {
  _ctor = previewers.fzf.help_tags,
  },
@@ -538,7 +534,7 @@ M.defaults.helptags = {
  ["--with-nth"] = "..-2",
  },
  previewer = {
- _ctor = previewers.builtin.help_file,
+ _ctor = previewers.builtin.help_tags,
  },
 }