Document Java 17/21/25 version matrix / 明确 Java 17/21/25 版本对应关系
Add English pages and replace the migration guide with a GUI API guide - Every page now exists in English and Simplified Chinese, linked to each other; Home and the sidebar list both languages. - The GUI migration guide is replaced by a GUI API Guide that documents the current API as a first release, without old-to-new tables. - 所有页面都提供英文和简体中文两个版本，并互相链接；首页和侧边栏 同时列出两种语言。 - 用 GUI API 指南取代 GUI 迁移指南：按首个正式版说明当前的 API， 不再包含新旧对照。