RFR: JDK-8312418: Add Elements.getEnumConstantBody [v3]

[Joe Darcy]

> Trivial implementation to get feedback on the proposed API.

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Change policy of default method.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14939/files
  - new: https://git.openjdk.org/jdk/pull/14939/files/c8eedff3..41c2448f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14939&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14939&range=01-02

  Stats: 20 lines in 2 files changed: 11 ins; 2 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/14939.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14939/head:pull/14939

PR: https://git.openjdk.org/jdk/pull/14939