[code-reflection] RFR: Make Quoted generic

[Paul Sandoz]

Make `Quoted` generic with an upper bound of `Op`. Modify `Op.ofLambda` to return `Quoted<JavaOp.LambdaOp>`.

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Commit messages:
 - Update Quoted doc.
 - Make Quoted generic.

Changes: https://git.openjdk.org/babylon/pull/845/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=845&range=00
  Stats: 121 lines in 25 files changed: 15 ins; 3 del; 103 mod
  Patch: https://git.openjdk.org/babylon/pull/845.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/845/head:pull/845

PR: https://git.openjdk.org/babylon/pull/845