Fix barbar integration with nvim-tree (#523)

- Add an offset to display NvimTree buffer in barbar.
It won't work correctly if you enable "vim.g.nvim_tree_quit_on_open".
- Add which-key support to barbar to enable missing mappings.

Co-authored-by: Christian Chiarulli <chris.machine@pm.me>

lua/lv-nvimtree/init.lua

@@ -20,6 +20,7 @@ vim.g.nvim_tree_indent_markers = 1 -- "0 by default, this option shows indent ma
 vim.g.nvim_tree_follow = 1 -- "0 by default, this option allows the cursor to be updated when entering a buffer
 vim.g.nvim_tree_auto_close = O.auto_close_tree -- 0 by default, closes the tree when it's the last window
 vim.g.nvim_tree_auto_ignore_ft = 'startify' --empty by default, don't auto open tree on specific filetypes.
+vim.g.nvim_tree_quit_on_open = 0 -- this doesn't play well with barbar
 local tree_cb = require'nvim-tree.config'.nvim_tree_callback
     vim.g.nvim_tree_bindings = {
       -- ["<CR>"] = ":YourVimFunction()<cr>",
@@ -63,3 +64,19 @@ vim.g.nvim_tree_icons = {
     git = {unstaged = "", staged = "✓", unmerged = "", renamed = "➜", untracked = ""},
     folder = {default = "", open = "", empty = "", empty_open = "", symlink = ""}
 }
+
+local view = require'nvim-tree.view'
+
+local _M = {}
+_M.toggle_tree = function()
+  if view.win_open() then
+    require'nvim-tree'.close()
+    require'bufferline.state'.set_offset(0)
+  else
+    require'bufferline.state'.set_offset(31, 'File Explorer')
+    require'nvim-tree'.find_file(true)
+  end
+
+end
+
+return _M