[code-reflection] RFR: Update the model of pattern matching when pattern variable identifier is underscore

[Mourad Abbay]

Update the generated code model of pattern matching when pattern variable identifier is "_"

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

Commit messages:
 - Update the model of pattern matching when pattern variable identifier is "_"

Changes: https://git.openjdk.org/babylon/pull/227/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=227&range=00
  Stats: 25 lines in 2 files changed: 23 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/babylon/pull/227.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/227/head:pull/227

PR: https://git.openjdk.org/babylon/pull/227