[jdk18] RFR: 8278948: compiler/vectorapi/reshape/TestVectorCastAVX1.java crashes in assembler

[Mai Đặng Quân Anh]

This patch fixes a crash spotted in `compiler/vectorapi/reshape/TestVectorCastAVX1.java` in mainline. The reason for the failure is the incorrect vector encoding of integer promotion operation leads to unsupported instruction `vpmovsxbd/vpmovsxwd ymm, xmm` on AVX1. For the same reason we currently cannot cast a short or byte vector to a 256-bit float vector on AVX1, so I also fixed that.

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Commit messages:
 - fix wrong vlen_enc

Changes: https://git.openjdk.java.net/jdk18/pull/46/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=46&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278948
  Stats: 17 lines in 1 file changed: 3 ins; 8 del; 6 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/46.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/46/head:pull/46

PR: https://git.openjdk.java.net/jdk18/pull/46