[code-reflection] Integrated: switching to new transformer pattern - ThreadsPhase

[Gary Frost]

Switched ThreadsPhase to use new transformer pattern.

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Commit messages:
 - switching to new transformer pattern - ThreadsPhase

Changes: https://git.openjdk.org/babylon/pull/764/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=764&range=00
  Stats: 183 lines in 8 files changed: 69 ins; 71 del; 43 mod
  Patch: https://git.openjdk.org/babylon/pull/764.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/764/head:pull/764

PR: https://git.openjdk.org/babylon/pull/764