VectorMask bitwise operations

[Paul Sandoz]

Thanks for looking at this.

I commented on your PR:

  https://github.com/openjdk/panama-vector/pull/212#pullrequestreview-1369260683

Paul.

> On Apr 1, 2023, at 7:33 AM, Quân Anh Mai <anhmdq at gmail.com> wrote:
> 
> Hi, 
> 
> Currently, there is no xor operation for VectorMask, and xnor is called eq, which seems not consistent with the other logical operations. I also noticed that each concrete mask type has a xor method. As a result, I propose adding VectorMask.xor and renaming VectorMask.eq to VectorMask.xorNot. What do you think?
> 
> Thanks a lot,
> Quan Anh