RFR: 8267614: Outline VarHandleGuards exact behavior checks

[Claes Redestad]

Extract some common behavior checks from the generated VarHandleGuards code to a package-private VarHandle method. This reduces the code size (-5.2kb lib/modules) and slightly improves startup, while being performance neutral on microbenchmarks.

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Commit messages:
 - Outline VarHandleGuard exact behavior checks

Changes: https://git.openjdk.java.net/jdk/pull/4165/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4165&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267614
  Stats: 338 lines in 3 files changed: 14 ins; 243 del; 81 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4165.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4165/head:pull/4165

PR: https://git.openjdk.java.net/jdk/pull/4165