[vectorIntrinsics] RFR: Load/store short vectors from/to char[]

[Paul Sandoz]

Methods to load/store a `ShortVector` from/to `char[]`. These methods may be useful for encoding/decoding characters.

Unclear if aliasing of `char[]` and `short[]` causes issues for the intrinsic or for Hotspot code gen.

Testing-wise, it was easier to explicitly clone and reify the relevant tests rather than trying to generalize the template and its template arguments to distinguish between the vector type and the array type.

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Commit messages:
 - Load/store short vectors from/to char[]

Changes: https://git.openjdk.java.net/panama-vector/pull/22/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=22&range=00
  Stats: 2782 lines in 69 files changed: 2279 ins; 496 del; 7 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/22.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/22/head:pull/22

PR: https://git.openjdk.java.net/panama-vector/pull/22