RFR: 6964: [Agent] Automatically open base module for accessing Unsafe on JDK 11+ [v3]

[Gunnar Morling]

> So here's a fresh take on the `Unsafe` / `add-opens` issue for JMC Agent. This still is using `Unsafe`, but I'm using the instrumentation API for opening up the base module within the agent itself, instead of requiring the user to do so. Ideally, we'd still get away from `Unsafe`, but this make the agent easier to use. This is still a draft, would do some more polishing if you all think it's the right approach. Feedback welcome!

Gunnar Morling has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - 6964: Refactor - Unifying handling of Java version
 - 6964: Automatically open base module for accessing Unsafe on JDK 11+

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Changes:
  - all: https://git.openjdk.java.net/jmc/pull/152/files
  - new: https://git.openjdk.java.net/jmc/pull/152/files/2fdedcb4..5d4792ff

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=152&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=152&range=01-02

  Stats: 6660 lines in 137 files changed: 5873 ins; 218 del; 569 mod
  Patch: https://git.openjdk.java.net/jmc/pull/152.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/152/head:pull/152

PR: https://git.openjdk.java.net/jmc/pull/152