[code-reflection] Integrated: [hat] Testing framework moved to hat.test

[Juan Fumero]

Refactor: testing framework moved from `oracle.code.hat` to `hat.test`

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Commit messages:
 - [hat] Testing framework moved to hat.test

Changes: https://git.openjdk.org/babylon/pull/616/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=616&range=00
  Stats: 60 lines in 20 files changed: 0 ins; 1 del; 59 mod
  Patch: https://git.openjdk.org/babylon/pull/616.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/616/head:pull/616

PR: https://git.openjdk.org/babylon/pull/616