[code-reflection] Integrated: More jextract prep

[Gary Frost]

As we move towards creating a jextracted opencl and cuda backends we need bld changes to support using jextract.

This is step one in that process.

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Commit messages:
 - More jextract prep

Changes: https://git.openjdk.org/babylon/pull/287/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=287&range=00
  Stats: 2865 lines in 5 files changed: 1250 ins; 1108 del; 507 mod
  Patch: https://git.openjdk.org/babylon/pull/287.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/287/head:pull/287

PR: https://git.openjdk.org/babylon/pull/287