JEP 401: Value Objects (Preview) merged to OpenJDK master

This pull request implements the first preview of JEP 401: Value Objects (Preview). This pull request also includes the implementation of JEP 539: Strict Field Initialization in the JVM (Preview). That work was implemented in the same code base because JEP 401 depends on strict field initialization.

此合并请求（Pull Request）实现了 JEP 401：值对象（预览版）的首次预览。该请求还包含了 JEP 539：JVM 中严格字段初始化（预览版）的实现。由于 JEP 401 依赖于严格字段初始化，因此这两项工作在同一个代码库中实现。

Sub-reviews, for spreading review debates are here:

• JDK-8317277: Java language implementation of value objects #31121
• JDK-8317278: JVM implementation of value objects #31122
• JDK-8317279: Standard library implementation of value objects #31123

为了分散评审讨论，相关的子评审链接如下：

• JDK-8317277：值对象的 Java 语言实现 #31121
• JDK-8317278：值对象的 JVM 实现 #31122
• JDK-8317279：值对象的标准库实现 #31123

This is the “master pull request” for the initial preview of JEP 401. Comments and review for a change this large will not scale well in a single pull request. This pull request serves as the vehicle for sign-off and integration into jdk/master. Review comments should be directed to the appropriate “sub-review pull request” listed above.

这是 JEP 401 初始预览版的“主合并请求”。对于如此大规模的变更，在单一合并请求中进行评论和评审难以高效扩展。此合并请求主要用于签署确认并集成到 jdk/master 分支中。评审意见应提交至上述对应的“子评审合并请求”中。

Note: The “sub-review pull requests” contain the same full set of code changes as this “master pull request” to preserve the full implementation context; the language compiler, JVM, and standard library changes are intertwined. The separate pull requests exist only to subdivide the review and related discussion by area.

注意：“子评审合并请求”包含与此“主合并请求”相同的完整代码变更集，以保持完整的实现上下文；因为语言编译器、JVM 和标准库的变更相互交织。拆分多个合并请求仅是为了按领域细分评审和相关讨论。

Any resulting code changes should be made in valhalla/lworld. valhalla/lworld is currently updated from jdk/master whenever a weekly jdk tag is created. At that time, code changes from valhalla/lworld will be propagated to this pull request and to all sub-review pull requests. Ultimately, review sign-off will be recorded on this “master pull request”, and the “sub-review pull requests” will be closed without integration.

任何后续的代码变更都应在 valhalla/lworld 中进行。每当创建每周 JDK 标签时，valhalla/lworld 都会从 jdk/master 进行更新。届时，来自 valhalla/lworld 的代码变更将同步到此主合并请求及所有子评审合并请求中。最终，评审确认将记录在此“主合并请求”上，而“子评审合并请求”将在不进行集成的情况下关闭。

This pull request has a large surface area and frequently conflicts with jdk/master. Refer to valhalla/lworld for the latest state of the project code, keeping in mind that it may lag several days behind jdk/master. Both repositories may be needed as references during review.

此合并请求涉及范围广泛，且经常与 jdk/master 产生冲突。请参考 valhalla/lworld 获取项目代码的最新状态，并注意它可能比 jdk/master 滞后几天。在评审过程中，可能需要同时参考这两个仓库。