RFR: 6996: Properly support converters

[Marcus Hirt]

Including simple test to verify that the resulting instrumented methods are ok.

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Commit messages:
 - 6996: Properly support converters

Changes: https://git.openjdk.java.net/jmc/pull/168/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jmc&pr=168&range=00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6996
  Stats: 7223 lines in 52 files changed: 5871 ins; 1044 del; 308 mod
  Patch: https://git.openjdk.java.net/jmc/pull/168.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/168/head:pull/168

PR: https://git.openjdk.java.net/jmc/pull/168