RFR: 8269674: Improve testing of parenthesized patterns

[Aggelos Biboudis]

Introduces a combo test (compile-time) for parenthesized patterns. Subsumes `test/langtools/tools/javac/patterns/Parenthesized.java`. 

Bugs addressed:
- `case (StringBox(String s1))` raised a parse error

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Commit messages:
 - 8269674: Add combo test and fix parenthesized

Changes: https://git.openjdk.org/jdk/pull/9344/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9344&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8269674
  Stats: 174 lines in 2 files changed: 169 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9344.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9344/head:pull/9344

PR: https://git.openjdk.org/jdk/pull/9344