RFR: 8265079: Implement VarHandle invoker caching [v2]

[Jorn Vernee]

> 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

Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:

  Review comments:
  - Use boolean instead of index for var handle cache

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3439/files
  - new: https://git.openjdk.java.net/jdk/pull/3439/files/df10dbdd..93681f77

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3439&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3439&range=00-01

  Stats: 14 lines in 1 file changed: 4 ins; 0 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3439.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3439/head:pull/3439

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