RFR: JDK-8317633: Modernize text.testlib.HexDumpReader

[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.

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

Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/16075/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16075&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317633
  Stats: 84 lines in 1 file changed: 12 ins; 62 del; 10 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