RFR: 8316426: Optimization for HexFormat.formatHex [v8]

[温绍锦]

> In the improvement of @cl4es PR #15591, the advantages of non-lookup-table were discussed.
> 
> But if the input is byte[], using lookup table can improve performance.
> 
> For HexFormat#formatHex(Appendable, byte[]) and HexFormat#formatHex(byte[]), If the length of byte[] is larger, the performance of table lookup will be improved more obviously.

温绍锦 has updated the pull request incrementally with one additional commit since the last revision:

  reduce the size of HexFormat##DIGITS, from 256 to 128

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15768/files
  - new: https://git.openjdk.org/jdk/pull/15768/files/8eff0ee4..2ed9ac37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15768&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15768&range=06-07

  Stats: 11 lines in 1 file changed: 0 ins; 8 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15768.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15768/head:pull/15768

PR: https://git.openjdk.org/jdk/pull/15768