feat: add TreePreOpen event (#3105)

* feat: Add `TreePreOpen` and `TreePreClose` events

* docs: Update docs for `TreePreOpen` and `TreePreClose` events

* chore: remove `TreePreClose` event and update dispatch of `TreePreOpen`

---------

Co-authored-by: Alexander Courtis <alex@courtis.org>

lua/nvim-tree/events.lua

@@ -8,6 +8,7 @@ M.Event = {
   Ready = "Ready",
   WillRenameNode = "WillRenameNode",
   NodeRenamed = "NodeRenamed",
+  TreePreOpen = "TreePreOpen",
   TreeOpen = "TreeOpen",
   TreeClose = "TreeClose",
   WillCreateFile = "WillCreateFile",
@@ -91,6 +92,11 @@ function M._dispatch_folder_removed(folder_name)
   dispatch(M.Event.FolderRemoved, { folder_name = folder_name })
 end
 
+--@private
+function M._dispatch_on_tree_pre_open()
+  dispatch(M.Event.TreePreOpen, nil)
+end
+
 --@private
 function M._dispatch_on_tree_open()
   dispatch(M.Event.TreeOpen, nil)