RFR: Data instrumentation plugin

[Alexandre Iline]

This adds "data coverage" module to JCov.
Data coverage is implemented with JDK class file API.
Older version, which was held as a plugin has been removed.
Necessary changes to JCov core are made to accommodate this new instrumentation mechanism.

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Commit messages:
 - fix for CODETOOLS-7903452
 - test fixes
 - adding data coverage code

Changes: https://git.openjdk.org/jcov/pull/39/files
 Webrev: https://webrevs.openjdk.org/?repo=jcov&pr=39&range=00
  Stats: 5953 lines in 90 files changed: 3847 ins; 2089 del; 17 mod
  Patch: https://git.openjdk.org/jcov/pull/39.diff
  Fetch: git fetch https://git.openjdk.org/jcov.git pull/39/head:pull/39

PR: https://git.openjdk.org/jcov/pull/39