[code-reflection] RFR: Support record pattern for generic records

[Mourad Abbay]

Support record pattern for generic records

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Commit messages:
 - Use externalize method in toString of RecordTypeRefImpl, MethodRefImpl and FieldRefImpl
 - Modify TypeVarRef.toString to print more info about type variable

Changes: https://git.openjdk.org/babylon/pull/240/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=240&range=00
  Stats: 6 lines in 3 files changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/babylon/pull/240.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/240/head:pull/240

PR: https://git.openjdk.org/babylon/pull/240