[code-reflection] Integrated: Moved some 'util' helpers into nested phase classes

[Gary Frost]

Moved sealed class heirarchy into nested classes (Ops and Phases) and moves util classes to the appropriate level of nesting

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Commit messages:
 - Moved some 'util' helpers into nested phase classes

Changes: https://git.openjdk.org/babylon/pull/793/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=793&range=00
  Stats: 4143 lines in 59 files changed: 1366 ins; 2557 del; 220 mod
  Patch: https://git.openjdk.org/babylon/pull/793.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/793/head:pull/793

PR: https://git.openjdk.org/babylon/pull/793