RFR: 8265079: Implement VarHandle invoker caching

[Claes Redestad]

On Mon, 12 Apr 2021 16:24:37 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> This patch implements 2 leftover TODOs for implementing var handle invoker MH caching (lambda forms for those were already shared/cached).
> 
> This piggybacks on the existing mechanism for method handle invoker caching.
> 
> Testing: Local testing `java/lang/invoke` tests. Tier 1-3
> 
> Thanks,
> Jorn

LGTM

`MethodHandles.varHandle(Exact)Invoker` might be somewhat obscure, but caching them like this is straightforward and basically free.

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Marked as reviewed by redestad (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/3439