feat(event): add TreeRendered (#2324)

* add TreeRendered event

* pass bufnr and winnr to TreeRendered event

---------

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

lua/nvim-tree/events.lua

@@ -18,6 +18,7 @@ M.Event = {
   FolderRemoved = "FolderRemoved",
   Resize = "Resize",
   TreeAttachedPost = "TreeAttachedPost",
+  TreeRendered = "TreeRendered",
 }
 
 local function get_handlers(event_name)
@@ -104,4 +105,9 @@ function M._dispatch_tree_attached_post(buf)
   dispatch(M.Event.TreeAttachedPost, buf)
 end
 
+--@private
+function M._dispatch_on_tree_rendered(bufnr, winnr)
+  dispatch(M.Event.TreeRendered, { bufnr = bufnr, winnr = winnr })
+end
+
 return M