IDLE: add a Unicode character browser

Feature or enhancement

IDLE has no way to browse or search for a Unicode character. Inserting one requires already knowing its code point (and typing an escape) or pasting it from another application.

Besides making characters easy to insert, such a tool is useful for learning about Unicode — exploring blocks, looking up a character's name, category, and other properties, and seeing how it is written as an escape, as UTF-8 bytes, as an XML or HTML reference, and in the normalization forms.

I propose a Character Browser, similar to KDE's kcharselect and GNOME Characters, added as a CharSelect extension on the Edit menu (available in both the Shell and the editor).

Features:

• A grid of Unicode blocks selected from a drop-down, scrollable, with hover and selection highlight.
• Search by character name substring, or by code point in many notations: U+2764, 0x2764, ❤, ❤, a bare hex/decimal number, \u/\U/\x/\N{...}/simple escapes, surrogate pairs, and a UTF-8 byte escape run.
• A detail panel with three tabs: an Overview (name, code point, decimal), a Repr tab (literal, Python escape, UTF-8 bytes, surrogate pair, XML and HTML references, \N{...}), and a Unicode tab (block, category, bidi, combining, East Asian width, mirrored, decomposition, numeric values, and normalization forms).
• Insert the character at the cursor of the editor or Shell (replacing any selection, and staying within the Shell's input area), or Copy it to the clipboard. Double-clicking a character in the grid inserts it.
• On the detail tabs, clicking a value copies it and double-clicking inserts it.

When opened with an editor selection, the browser seeds the search with it.

A PR will follow.

Related (not a duplicate): #80648 (help with invisible characters).

Linked PRs

• gh-152945

Bắt đầu bằng việc xem xét tiện ích mở rộng CharSelect được đề xuất trong menu Edit của IDLE và PR gh-152945 được liên kết. So sánh phần triển khai với các yêu cầu đã liệt kê về duyệt, tìm kiếm, thông tin chi tiết, chèn và sao chép Unicode cho cả Shell và trình soạn thảo; hoàn tất nghĩa là phạm vi đã thống nhất được triển khai và xác minh.