[code-reflection] RFR: Code model from method reference

[Paul Sandoz]

Obtain a code model from method reference. The implementation is simple and resolves the method reference to an instance of `Method`, and returns the result of `Method::getCodeModel`.

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Commit messages:
 - Code model from method reference.

Changes: https://git.openjdk.org/babylon/pull/34/files
 Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=34&range=00
  Stats: 29 lines in 3 files changed: 28 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/babylon/pull/34.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/34/head:pull/34

PR: https://git.openjdk.org/babylon/pull/34