RFR: CODETOOLS-7903355: JMH: Drop support for JDK 7

[Aleksey Shipilev]

Head JDK 20-ea does not support building with -source/target 7 anymore. JDK 7 is very old and unlikely to be used widely. We can bump the minimal version to JDK 8 to get... ahem... all the new features that release brings! 

If you have a strong opinion that we should **not** drop JDK 7 support, please speak up soon.

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Commit messages:
 - Use ASM5 to get invokedynamic parsed
 - Fix
 - Fix

Changes: https://git.openjdk.org/jmh/pull/86/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=86&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903355
  Stats: 223 lines in 59 files changed: 7 ins; 96 del; 120 mod
  Patch: https://git.openjdk.org/jmh/pull/86.diff
  Fetch: git fetch https://git.openjdk.org/jmh pull/86/head:pull/86

PR: https://git.openjdk.org/jmh/pull/86