[code-reflection] Integrated: Added inversion of control pattern so capabilities can coordinate with jextract

[Gary Frost]

simplified bld script, by allowing  'cababilities' implementing 'jextractable' to coordinate directly with jextract.

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Commit messages:
 - Added inversion of control pattern so capabilities can coordinate with jextract

Changes: https://git.openjdk.org/babylon/pull/313/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=313&range=00
  Stats: 67 lines in 2 files changed: 36 ins; 25 del; 6 mod
  Patch: https://git.openjdk.org/babylon/pull/313.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/313/head:pull/313

PR: https://git.openjdk.org/babylon/pull/313