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/explorer/init.lua

@@ -530,7 +530,7 @@ function Explorer:place_cursor_on_node()
 end
 
 ---Api.tree.get_nodes
----@return Node
+---@return nvim_tree.api.Node
 function Explorer:get_nodes()
   return self:clone()
 end