[code-reflection] RFR: Unify code that generates code model of switch statement and expression

[Mourad Abbay]

Unify code that generates code model of switch statement and expression

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Commit messages:
 - Refactor

Changes: https://git.openjdk.org/babylon/pull/220/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=220&range=00
  Stats: 389 lines in 1 file changed: 109 ins; 202 del; 78 mod
  Patch: https://git.openjdk.org/babylon/pull/220.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/220/head:pull/220

PR: https://git.openjdk.org/babylon/pull/220