add classic, migrating nodes classes

lua/nvim-tree/node/link.lua

@@ -0,0 +1,8 @@
+local Object = require("nvim-tree.classic")
+
+---@class (exact) LinkNode: Object
+---@field link_to string
+---@field protected fs_stat_target uv.fs_stat.result
+local LinkNode = Object:extend()
+
+return LinkNode