RFR: 8037397: Lost nested character class after intersection &&

[Ian Graves]

Bug fix with the intersection `&&` operator in regex patterns. In JDK-8037397, some character classes on the right hand side of the operator are dropped in cases where nested `[..]` classes are used with non "nested" ones.

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Commit messages:
 - Fixing a regex intersection bug that drops expressions on the right hand side

Changes: https://git.openjdk.java.net/jdk/pull/3291/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3291&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8037397
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3291.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3291/head:pull/3291

PR: https://git.openjdk.java.net/jdk/pull/3291