Give clearer information about platform-specific differences on the locale page

The locale module has various limitations and differences depending on the platform. Most notably, Windows lacks some functionality.
It would be helpful to add a note about this in the opening section.
Also, nl_langinfo is not available on Windows and the sentence about "not available on all systems" is lost in the first paragraph. I suggest making it a Note and doing the same for the other places where platform differences/limitations are noted.

Linked PRs

• gh-118217

從 locale 模組文件頁面開始，檢查開頭部分以及描述平台差異的段落。查看 nl_langinfo 項目和其他關於限制的說明，然後讓平台特定資訊始終以註記的形式清楚呈現。完成標準是：Windows 的限制和可用性差異在整個頁面中都清楚明確。