[vectorIntrinsics] RFR: Add @since 19 tags

[Paul Sandoz]

Add @since 19 tags to newly added APIs.

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Commit messages:
 - Add since JavaDoc tags

Changes: https://git.openjdk.java.net/panama-vector/pull/200/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=200&range=00
  Stats: 73 lines in 11 files changed: 65 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/200.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/200/head:pull/200

PR: https://git.openjdk.java.net/panama-vector/pull/200