RFR: CODETOOLS-7903548: Allow plugins to be compiled into the jcov.jar [v2]

[Alexandre Iline]

> Allow plugins to be compiled into the jcov.jar

Alexandre Iline has updated the pull request incrementally with one additional commit since the last revision:

  reverting changes to main build, changing plugin builds instead

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Changes:
  - all: https://git.openjdk.org/jcov/pull/42/files
  - new: https://git.openjdk.org/jcov/pull/42/files/f0507c7c..3edc8d6e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jcov&pr=42&range=01
 - incr: https://webrevs.openjdk.org/?repo=jcov&pr=42&range=00-01

  Stats: 82 lines in 3 files changed: 12 ins; 62 del; 8 mod
  Patch: https://git.openjdk.org/jcov/pull/42.diff
  Fetch: git fetch https://git.openjdk.org/jcov.git pull/42/head:pull/42

PR: https://git.openjdk.org/jcov/pull/42