RFR: 8251989: Hex formatting and parsing utility [v3]

[Roger Riggs]

> java.util.HexFormat utility:
> 
>  - Format and parse hexadecimal strings, with parameters for delimiter, prefix, suffix and upper/lowercase
>  - Static factories and builder methods to create HexFormat copies with modified parameters.
>  - Consistent naming of methods for conversion of byte arrays to formatted strings and back: formatHex and parseHex
>  - Consistent naming of methods for conversion of primitive types: toHexDigits... and fromHexDigits...
>  - Prefix and suffixes now apply to each formatted value, not the string as a whole
>  - Using java.util.Appendable as a target for buffered conversions so output to Writers and PrintStreams
>    like System.out are supported in addition to StringBuilder. (IOExceptions are converted to unchecked exceptions)
>  - Immutable and thread safe, a "value-based" class
> 
> See the [HexFormat
> javadoc](http://cr.openjdk.java.net/~rriggs/8251989-hex-formatter/java.base/java/util/HexFormat.html) for details.
> Review comments and suggestions welcome.

Roger Riggs has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev
excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since
the last revision:

 - Added assertions to testVariableLength and samples
 - Merge branch 'master' into 8251989-hex-formatter
 - temp updates
 - Various code review comments, rename UpperCase and LowerCase methods to match Character, remove unnecessary Class name
   qualifications, etc.
 - 8251989: Hex formatting and parsing utility

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/482/files
  - new: https://git.openjdk.java.net/jdk/pull/482/files/3170b498..ec334dbc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=482&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=482&range=01-02

  Stats: 39353 lines in 906 files changed: 21925 ins; 9958 del; 7470 mod
  Patch: https://git.openjdk.java.net/jdk/pull/482.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/482/head:pull/482

PR: https://git.openjdk.java.net/jdk/pull/482