[jdk25u] RFR: 8365772: RISC-V: correctly prereserve NaN payload when converting from float to float16 in vector way

[Hamlin Li]

8365772: RISC-V: correctly prereserve NaN payload when converting from float to float16 in vector way

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Commit messages:
 - Backport 32df2d17f3c0407ad7e90eacfdc0fd7a65f67551

Changes: https://git.openjdk.org/jdk25u/pull/137/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk25u&pr=137&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365772
  Stats: 66 lines in 3 files changed: 46 ins; 0 del; 20 mod
  Patch: https://git.openjdk.org/jdk25u/pull/137.diff
  Fetch: git fetch https://git.openjdk.org/jdk25u.git pull/137/head:pull/137

PR: https://git.openjdk.org/jdk25u/pull/137