[vectorIntrinsics+compress] RFR: 8274664: Add support for compress/expand api methods

[Sandhya Viswanathan]

Add support for the cross lane operations to compress/expand the lane elements of a vector selecting lanes under the control of a mask. The remaining lanes of the destination vector could be either set to zero or get the value from corresponding elements of the background vector.
The following methods are added:
 public abstract Vector<E> compress(VectorMask<E> m);
 public abstract Vector<E> compress(VectorMask<E> m, Vector<E> v);
 public abstract Vector<E> expand(VectorMask<E> m);
 public abstract Vector<E> expand(VectorMask<E> m, Vector<E> v);

-------------

Commit messages:
 - 8274664: Add support for compress/expand api methods

Changes: https://git.openjdk.java.net/panama-vector/pull/143/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-vector&pr=143&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274664
  Stats: 7010 lines in 72 files changed: 7010 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-vector/pull/143.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-vector pull/143/head:pull/143

PR: https://git.openjdk.java.net/panama-vector/pull/143