feat(#2948): add custom decorators, :help nvim-tree-decorators (#2996)

* feat(#2948): add UserDecorator, proof of concept

* feat(#2948): add UserDecorator, proof of concept

* feat(#2948): add UserDecorator, proof of concept

* feat(#2948): add UserDecorator

* feat(#2948): add UserDecorator

* feat(#2948): add UserDecorator

* feat(#2948): add Decorator node icon override

* feat(#2948): add nvim_tree.api.* node classes

* feat(#2948): extract _meta following nvim pattern

* feat(#2948): extract _meta following nvim pattern

* feat(#2948): add decorator registry and order

* feat(#2948): add decorator registry and order

* feat(#2948): tidy

* feat(#2948): document API

* feat(#2948): document API

* feat(#2948): document API

* feat(#2948): pass api nodes to user decorators

* feat(#2948): document API

* feat(#2948): use renderer.decorators to define order and register

* feat(#2948): tidy decorator args and complete documentation

* feat(#2948): decorator classes specified by prefix rather than suffix

* feat(#2948): improve doc

* feat(#2948): improve doc

* feat(#2948): improve doc

* feat(#2948): additional user decorator safety

* feat(#2948): create nvim_tree.api.decorator.UserDecorator class in API, add :extend

* feat(#2948): improve doc

lua/nvim-tree/node/directory.lua

@@ -271,18 +271,20 @@ function DirectoryNode:highlighted_name()
 end
 
 ---Create a sanitized partial copy of a node, populating children recursively.
----@return DirectoryNode cloned
-function DirectoryNode:clone()
-  local clone        = Node.clone(self) --[[@as DirectoryNode]]
+---@param api_nodes table<number, nvim_tree.api.Node>? optional map of uids to api node to populate
+---@return nvim_tree.api.DirectoryNode cloned
+function DirectoryNode:clone(api_nodes)
+  local clone        = Node.clone(self, api_nodes) --[[@as nvim_tree.api.DirectoryNode]]
 
   clone.has_children = self.has_children
-  clone.group_next   = nil
   clone.nodes        = {}
   clone.open         = self.open
-  clone.hidden_stats = nil
 
+  local clone_child
   for _, child in ipairs(self.nodes) do
-    table.insert(clone.nodes, child:clone())
+    clone_child = child:clone(api_nodes)
+    clone_child.parent = clone
+    table.insert(clone.nodes, clone_child)
   end
 
   return clone