RFR: 8286849: Use @Stable for generic repositories

[liach]

On Tue, 17 May 2022 04:40:50 GMT, liach <duke at openjdk.java.net> wrote:

> Generic repositories, the implementation detail for generic information in core reflection, can be updated to use the `@Stable` annotation to replace their `volatile` access. Their existing accessor code is already safe, reading the cache fields only once.
> 
> In addition, fixed potentially non-thread-safe `genericInfo` access in `Method`, `Field`, and `RecordComponent`.

This should offer slight performance benefit if a reflection object has its generic information accessed frequently, as reading a stable field is faster than reading a volatile field for cached objects. If the `genericInfo` fields are updated by JVMTI then they need to be declared `volatile` instead. In addition, some of the `genericInfo` fields may have been not thread-safe for their multiple field reads.

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PR: https://git.openjdk.java.net/jdk/pull/8742