[jdk21u-dev] RFR: 8317633: Modernize text.testlib.HexDumpReader

[Goetz Lindenmaier]

I backport this for parity with 21.0.11-oracle.

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Commit messages:
 - Backport 8e0686b0658eb593bdf36e1c179a4b156fee26bf

Changes: https://git.openjdk.org/jdk21u-dev/pull/2576/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2576&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317633
  Stats: 87 lines in 1 file changed: 12 ins; 58 del; 17 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2576.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2576/head:pull/2576

PR: https://git.openjdk.org/jdk21u-dev/pull/2576