[code-reflection] RFR: Rename Op.ofQuotable to Op.ofLambda.

[Paul Sandoz]

Rename `Op.ofQuotable` to `Op.ofLambda`.

A subsequent PR will make changes to other areas where quotable is used to mean reflectable lambda expression or method reference.

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Commit messages:
 - Doc update.
 - Rename Op.ofQuotable to Op.ofLambda.

Changes: https://git.openjdk.org/babylon/pull/843/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=843&range=00
  Stats: 94 lines in 26 files changed: 1 ins; 11 del; 82 mod
  Patch: https://git.openjdk.org/babylon/pull/843.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/843/head:pull/843

PR: https://git.openjdk.org/babylon/pull/843