[code-reflection] RFR: Change the model of the default label of switch

[Mourad Abbay]

Model default label of switch as a body that yield true, this makes the modeling consistent for all labels.

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Commit messages:
 - Change the model of the default label of switch

Changes: https://git.openjdk.org/babylon/pull/223/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=223&range=00
  Stats: 169 lines in 6 files changed: 55 ins; 0 del; 114 mod
  Patch: https://git.openjdk.org/babylon/pull/223.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/223/head:pull/223

PR: https://git.openjdk.org/babylon/pull/223