RFR: 8266317: Vector API enhancements [v2]

[Paul Sandoz]

> This PR contains API and implementation changes for [JEP-414 Vector API (Second Incubator)](https://openjdk.java.net/jeps/414), in preparation for when targeted.
> 
> Enhancements are made to the API for the support of operations on characters, such as for UTF-8 character decoding. Specifically, methods for loading/storing a `short` vector from/to a `char[]` array, and new vector comparison operators for unsigned comparisons with integral vectors. The x64 implementation is enhanced to supported unsigned comparisons.
> 
> Enhancements are made to the API for loading/storing a `byte` vector from/to a `boolean[]` array.
> 
> The testing of loads/stores can be expanded for scatter/gather, but before doing that i think some refactoring of the tests is required to reposition tests in the right classes. I would like to do that work after integration of the PR.

Paul Sandoz has updated the pull request incrementally with one additional commit since the last revision:

  Rename method.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3803/files
  - new: https://git.openjdk.java.net/jdk/pull/3803/files/de210a88..93b093c1

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3803&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3803&range=00-01

  Stats: 7 lines in 7 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3803.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3803/head:pull/3803

PR: https://git.openjdk.java.net/jdk/pull/3803