RFR: 6964: [Agent] Automatically open base module for accessing Unsafe on JDK 11+ [v2]

[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 refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  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/1e7960c3..2fdedcb4

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jmc&pr=152&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jmc&pr=152&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 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