[vectorIntrinsics] RFR: Compress/expand op spec.

[Paul Sandoz]

Update the compress/expand operator specification.

I have retained the "_BITS" qualifier so as to more clearly differentiate from the method names, `compress` and `expand`, for the cross-lane compress and expand operations.

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Commit messages:
 - Compress/expand op spec.

Changes: https://git.openjdk.java.net/panama-vector/pull/196/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=196&range=00
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/196.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/196/head:pull/196

PR: https://git.openjdk.java.net/panama-vector/pull/196