RFR: 8309515: Stale cached data from Matcher.namedGroups() after Matcher.usePattern()

[Raffaello Giulietti]

The cached `namedGroup` field must be invalidated during an invocation of `Matcher.usePattern()`

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Commit messages:
 - 8309515: Stale cached data from Matcher.namedGroups() after Matcher.usePattern()

Changes: https://git.openjdk.org/jdk/pull/14350/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14350&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309515
  Stats: 24 lines in 2 files changed: 23 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14350.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14350/head:pull/14350

PR: https://git.openjdk.org/jdk/pull/14350