RFR: JDK-8317633: Modernize text.testlib.HexDumpReader [v2]

[Justin Lu]

> Please review this PR which cleans up the static test utility class _HexDumpReader_.
> 
> This cleans up the code by replacing the nested _ByteArrayBuilder_ class with _HexFormat_, and simplifies the File processing by using a stream. Changes were tested to ensure that the _text_ tests are still getting equivalent ByteArrayInputStreams as before.

Justin Lu has updated the pull request incrementally with one additional commit since the last revision:

  Reflect review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16075/files
  - new: https://git.openjdk.org/jdk/pull/16075/files/498b9096..6081b208

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16075&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16075&range=00-01

  Stats: 28 lines in 1 file changed: 10 ins; 6 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/16075.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16075/head:pull/16075

PR: https://git.openjdk.org/jdk/pull/16075