refactor: improve API readability and tidy actions submodules (#2593)

* refactor: improve API readability, tidy actions modules

* Apply requested changes

* `actions/reloaders/reloaders.lua` -> `actions/reloaders.lua`

---------

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

lua/nvim-tree/actions/root/init.lua

@@ -0,0 +1,10 @@
+local M = {}
+
+M.change_dir = require "nvim-tree.actions.root.change-dir"
+M.dir_up = require "nvim-tree.actions.root.dir-up"
+
+function M.setup(opts)
+  M.change_dir.setup(opts)
+end
+
+return M