IDLE: add a token browser

Seeing how source is split into tokens helps in learning how Python's tokenizer works and in debugging tokenizer-dependent behavior, but IDLE offers no way to inspect the token stream.

I propose a Token Browser added as an extension on the Tools menu (Shell and editor). It shows the output of tokenize for the current window in a ttk.Treeview — one row per token with its type, string, and range.

Interaction:

• Selecting a row highlights the corresponding source in the editor.
• Double-clicking a row moves the editor cursor to that token.
• The browser follows the editor: a selection selects every overlapping token row, and the cursor alone selects the single token containing it.
• Scope is the editor selection if there is one, else the Shell's current input, else the whole window.

A PR will follow.

Linked PRs

• gh-152946

從 Python 的 tokenize 輸出以及 Shell 和編輯器的 Tools 選單中的 IDLE 擴充功能入口點開始。檢視 ttk.Treeview 如何表示 token 類型、字串和範圍，然後驗證 issue 中描述的選取、雙擊、游標和作用域行為。完成的標準是瀏覽器跟隨目前的視窗，並將 token 列對應到原始碼位置；gh-152946 已作為後續 PR 連結。