add a __tostring method to every object (#1534)

* added a stupid __tostring to every object

* moved every __tostring to just after the :extend() call

---------

Co-authored-by: Adam <adamdharrison@gmail.com>
(cherry picked from commit 880e7f1fa1521cdf176f44627a27c901e187058e)

data/core/doc/highlighter.lua

@@ -7,6 +7,7 @@ local Object = require "core.object"
 
 local Highlighter = Object:extend()
 
+function Highlighter:__tostring() return "Highlighter" end
 
 function Highlighter:new(doc)
   self.doc = doc
@@ -126,5 +127,4 @@ function Highlighter:each_token(idx)
   return tokenizer.each_token(self:get_line(idx).tokens)
 end
 
-
 return Highlighter

data/core/doc/init.lua

@@ -8,6 +8,7 @@ local common = require "core.common"
 ---@class core.doc : core.object
 local Doc = Object:extend()
 
+function Doc:__tostring() return "Doc" end
 
 local function split_lines(text)
   local res = {}