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

从 locale 模块文档页面开始，检查其开头部分以及描述平台差异的段落。查看 nl_langinfo 条目和其他关于限制的说明，然后让平台特定信息始终以注释的形式清晰呈现。完成标准是：Windows 的限制和可用性差异在整个页面中都清晰明确。