feat(event): add TreeAttachedPost (#1877)

* feat(event): add OnAttachPost

* feat(event): add TreeAttachPost

* feat(event): add TreeAttachPost

* feat(event): TreeAttachedPost fired after all mappings created, not just on_attach

lua/nvim-tree/events.lua

@@ -15,6 +15,7 @@ M.Event = {
   FolderCreated = "FolderCreated",
   FolderRemoved = "FolderRemoved",
   Resize = "Resize",
+  TreeAttachedPost = "TreeAttachedPost",
 }
 
 local function get_handlers(event_name)
@@ -86,6 +87,11 @@ function M._dispatch_on_tree_resize(size)
   dispatch(M.Event.Resize, size)
 end
 
+--@private
+function M._dispatch_tree_attached_post(buf)
+  dispatch(M.Event.TreeAttachedPost, buf)
+end
+
 --- @deprecated
 function M.on_nvim_tree_ready(handler)
   M.subscribe(M.Event.Ready, handler)