fix: remove nested for_each_tree in TSTreeView (#26331)

Problem:
`LanguageTree:for_each_tree` calls itself for child nodes, so when we
calls `for_each_tree` inside `for_each_tree`, this quickly leads to
exponential tree calls.

Solution:
Use `pairs(child:trees())` directly in this case, as we don't need the
extra callback for each children, this is already handled from the outer
`for_each_tree` call

(cherry picked from commit 0712a4c085)

Co-authored-by: Pham Huy Hoang <hoangtun0810@gmail.com>

runtime/lua/vim/treesitter/playground.lua

@@ -106,17 +106,17 @@ function TSPlayground:new(bufnr, lang)
   parser:for_each_tree(function(parent_tree, parent_ltree)
     local parent = parent_tree:root()
     for _, child in pairs(parent_ltree:children()) do
-      child:for_each_tree(function(tree, ltree)
+      for _, tree in pairs(child:trees()) do
         local r = tree:root()
         local node = assert(parent:named_descendant_for_range(r:range()))
         local id = node:id()
         if not injections[id] or r:byte_length() > injections[id].root:byte_length() then
           injections[id] = {
-            lang = ltree:lang(),
+            lang = child:lang(),
             root = r,
           }
         end
-      end)
+      end
     end
   end)