[code-reflection] RFR: Reduce Op writing to text methods.

[Paul Sandoz]

Reduce the methods on op for writing to text down to one, `toText`. Ensure all other functionality is located on `OpWriter`.

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Commit messages:
 - Reduce Op writing to text methods.

Changes: https://git.openjdk.org/babylon/pull/488/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=488&range=00
  Stats: 291 lines in 53 files changed: 24 ins; 49 del; 218 mod
  Patch: https://git.openjdk.org/babylon/pull/488.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/488/head:pull/488

PR: https://git.openjdk.org/babylon/pull/488