RFR: 8065554: MatchResult should provide values of named-capturing groups

[Raffaello Giulietti]

Add support for named groups to java.util.regex.MatchResult

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Commit messages:
 - 8065554: MatchResult should provide values of named-capturing groups

Changes: https://git.openjdk.org/jdk/pull/10000/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10000&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8065554
  Stats: 554 lines in 4 files changed: 502 ins; 15 del; 37 mod
  Patch: https://git.openjdk.org/jdk/pull/10000.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10000/head:pull/10000

PR: https://git.openjdk.org/jdk/pull/10000