RFR: 8132995: Matcher$ImmutableMatchResult should be optimized to reduce space usage [v2]

[Raffaello Giulietti]

> When appropriate and useful, copies only the relevant portion of the `CharSequence` to the match result.

Raffaello Giulietti has updated the pull request incrementally with one additional commit since the last revision:

  Added some randomness in tests.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/13231/files
  - new: https://git.openjdk.org/jdk/pull/13231/files/7d6aba38..160b970a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13231&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13231&range=00-01

  Stats: 38 lines in 1 file changed: 24 ins; 8 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/13231.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13231/head:pull/13231

PR: https://git.openjdk.org/jdk/pull/13231