[vectorIntrinsics] RFR: 8281562:[vectorapi] Add support for popcount operation

[Smita Kamath]

8281562:[vectorapi] Add support for popcount operation

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Commit messages:
 - Add support for popcount operation for Integer and Long types.

Changes: https://git.openjdk.java.net/panama-vector/pull/173/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=173&range=00
  Stats: 181 lines in 8 files changed: 181 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/173.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/173/head:pull/173

PR: https://git.openjdk.java.net/panama-vector/pull/173