RFR: 8264514: HexFormat implementation tweaks [v2]

[Raffaello Giulietti]

> Please review these small tweaks.
> 
> For background information see [1](https://mail.openjdk.java.net/pipermail/core-libs-dev/2021-March/075822.html)
> 
> Greetings
> Raffaello

Raffaello Giulietti has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3295/files
  - new: https://git.openjdk.java.net/jdk/pull/3295/files/123f3101..21e7402b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3295&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3295&range=00-01

  Stats: 67 lines in 1 file changed: 26 ins; 10 del; 31 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3295.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3295/head:pull/3295

PR: https://git.openjdk.java.net/jdk/pull/3295