[vectorIntrinsics] RFR: 8275025: Unable to inline vectmask convert

[Ningsheng Jian]

JDK-8274631 introduced a fix with typo, which blocked all vector mask cast operations, since currently a vector mask type is also a vector type (See Type::isa_vect()).

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Commit messages:
 - 8275025: Unable to inline vectmask convert

Changes: https://git.openjdk.java.net/panama-vector/pull/151/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=151&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275025
  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/151.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/151/head:pull/151

PR: https://git.openjdk.java.net/panama-vector/pull/151