[code-reflection] Integrated: Hat more maven pom cleanup

[Gary Frost]

Discovered how to run cmake from maven in generate-sources phase. So we no longer have to call cmake manually before building with maven.

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Commit messages:
 - added -Popengl,opencl activations
 - cmake jextract added to maven pom.xml generate-sources
 - Commenting out dumping of vars
 - ffi backends use ffi-cmake-build-debug dir
 - create activations for opencl,opengl and cuda

Changes: https://git.openjdk.org/babylon/pull/402/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=402&range=00
  Stats: 436 lines in 13 files changed: 181 ins; 199 del; 56 mod
  Patch: https://git.openjdk.org/babylon/pull/402.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/402/head:pull/402

PR: https://git.openjdk.org/babylon/pull/402