RFR: 8132995: Matcher$ImmutableMatchResult should be optimized to reduce space usage [v3]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Adjusted incorrect logic in results().
   Added tests for results().
   Refined capturing logic when there's no match.
 - Merge branch 'master' into JDK-8132995
 - Adjusted erroneous logic in results().
   Added tests for results().
 - Added some randomness in tests.
 - 8132995: Matcher should be optimized to reduce space usage

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/13231/files
  - new: https://git.openjdk.org/jdk/pull/13231/files/160b970a..4b8ead1d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13231&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13231&range=01-02

  Stats: 456167 lines in 5146 files changed: 374095 ins; 45331 del; 36741 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