RFR: 8268151: Vector API toShuffle optimization

[Sandhya Viswanathan]

The Vector API toShuffle method can be optimized  using existing vector conversion intrinsic.

The following changes are made:
1) vector.toShuffle java implementation is changed to call VectorSupport.convert.
2) The conversion intrinsic (inline_vector_convert()) in vectorIntrinsics.cpp is changed to allow shuffle as a destination type.
3) The shuffle.toVector intrinsic (inline_vector_shuffle_to_vector()) in vectorIntrinsics.cpp now explicitly generates conversion node instead of performing conversion during unbox. This is to remove unnecessary boxing during back to back vector.toShuffle and shuffle.toVector calls. 

Best Regards,
Sandhya

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Commit messages:
 - toShuffle optimization

Changes: https://git.openjdk.java.net/jdk/pull/4326/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4326&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268151
  Stats: 393 lines in 34 files changed: 314 ins; 42 del; 37 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4326.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4326/head:pull/4326

PR: https://git.openjdk.java.net/jdk/pull/4326