[code-reflection] RFR: Use Op.ofQuoted

[Paul Sandoz]

The `Quotable` interface was modified to become a marker interface. To obtain the corresponding `Quoted`  instance (and the code model) we now need to call `Op.ofQuotable()`

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Commit messages:
 - Use Op not CoreOp
 - Use Op.ofQuoted.

Changes: https://git.openjdk.org/babylon/pull/304/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=304&range=00
  Stats: 6 lines in 4 files changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/babylon/pull/304.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/304/head:pull/304

PR: https://git.openjdk.org/babylon/pull/304