[code-reflection] RFR: Unary plus

[Paul Sandoz]

Support unary plus operator. No need to explicitly model as it has no direct operational semantics.

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Commit messages:
 - Unary plus operator
 - Unary plus operator

Changes: https://git.openjdk.org/babylon/pull/213/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=213&range=00
  Stats: 92 lines in 2 files changed: 90 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/babylon/pull/213.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/213/head:pull/213

PR: https://git.openjdk.org/babylon/pull/213