RFR: 8354522: Clones of DecimalFormat cause interferences when used concurrently [v3]

[Johannes Graham]

> The `DigitList` class used in `DecimalFormat` does not reset the `data` array in its clone method. This can cause interference when clones are used concurrently.

Johannes Graham has updated the pull request incrementally with one additional commit since the last revision:

  Tune the test to shorten run-time, update comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/24598/files
  - new: https://git.openjdk.org/jdk/pull/24598/files/880b2d89..61332647

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24598&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24598&range=01-02

  Stats: 34 lines in 2 files changed: 24 ins; 0 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/24598.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24598/head:pull/24598

PR: https://git.openjdk.org/jdk/pull/24598