feat(lsp): add snippet API (#25301)

runtime/lua/vim/lsp/util.lua

@@ -616,35 +616,7 @@ function M.parse_snippet(input)
     return input
   end
 
-  --- @param node vim.snippet.Node<any>
-  --- @return string
-  local function node_to_string(node)
-    local insert_text = {}
-    if node.type == snippet.NodeType.Snippet then
-      for _, child in
-        ipairs((node.data --[[@as vim.snippet.SnippetData]]).children)
-      do
-        table.insert(insert_text, node_to_string(child))
-      end
-    elseif node.type == snippet.NodeType.Choice then
-      table.insert(insert_text, (node.data --[[@as vim.snippet.ChoiceData]]).values[1])
-    elseif node.type == snippet.NodeType.Placeholder then
-      table.insert(
-        insert_text,
-        node_to_string((node.data --[[@as vim.snippet.PlaceholderData]]).value)
-      )
-    elseif node.type == snippet.NodeType.Text then
-      table.insert(
-        insert_text,
-        node
-          .data --[[@as vim.snippet.TextData]]
-          .text
-      )
-    end
-    return table.concat(insert_text)
-  end
-
-  return node_to_string(parsed)
+  return tostring(parsed)
 end
 
 --- Sorts by CompletionItem.sortText.