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/tree/init.lua

@@ -0,0 +1,15 @@
+local M = {}
+
+M.find_file = require "nvim-tree.actions.tree.find-file"
+M.modifiers = require "nvim-tree.actions.tree.modifiers"
+M.open = require "nvim-tree.actions.tree.open"
+M.toggle = require "nvim-tree.actions.tree.toggle"
+
+function M.setup(opts)
+  M.find_file.setup(opts)
+  M.modifiers.setup(opts)
+  M.open.setup(opts)
+  M.toggle.setup(opts)
+end
+
+return M