[jdk21u-dev] RFR: 8311939: Excessive allocation of Matcher.groups array

[Rui Li]

A clean backport for https://bugs.openjdk.org/browse/JDK-8311939.

This improves perf by not allocating excessive `groups` array. Tests are running. In tip for over 2 years and no related issues reported. Low risk.

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Commit messages:
 - Backport 32efd23c5d59c03a6376c92c63f5947e961ee24e

Changes: https://git.openjdk.org/jdk21u-dev/pull/2159/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2159&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311939
  Stats: 68 lines in 3 files changed: 64 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2159.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2159/head:pull/2159

PR: https://git.openjdk.org/jdk21u-dev/pull/2159