refactor: simplify opening file in new tab

fixes #1271. Also fixes opening a file in new tab when close_on_open was
true.

This introduces breaking change since we don't do any extra behavior
and let the buffer be opened by the tree.
The previous behavior was a bit old and i believe this should've been
fixed by now.
Reference this commit if unexpected behavior appears while opening files
in new tabs from nvim-tree.

lua/nvim-tree/view.lua

@@ -254,7 +254,7 @@ end
 function M.is_visible(opts)
   if opts and opts.any_tabpage then
     for _, v in pairs(M.View.tabpages) do
-      if a.nvim_win_is_valid(v.winnr) then
+      if v.winnr and a.nvim_win_is_valid(v.winnr) then
         return true
       end
     end