[code-reflection] RFR: Unreachable switch expression block

[Paul Sandoz]

This fixes the generated code model for an unreachable edge case discussed in PR #257:

String s = switch (n) {
    case 3 -> { while (true); }
    default -> " Hello!";
};

-------------

Commit messages:
 - Unreachable switch expression block.

Changes: https://git.openjdk.org/babylon/pull/260/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=260&range=00
  Stats: 50 lines in 2 files changed: 42 ins; 7 del; 1 mod
  Patch: https://git.openjdk.org/babylon/pull/260.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/260/head:pull/260

PR: https://git.openjdk.org/babylon/pull/260