[vector] Change Vector/Species/Shape from interface to public abstract classes

[Paul Sandoz]

Hi,

I propose to change Vector/Species/Shape from interface to public abstract classes. This allows us to control all the concrete implementations. We can revisit when we have value types and sealed classes.

The public type-specific vectors, such as IntVector, were already public abstract classes. Mask/Shuffle were previously made public abstract classes for C2 optimization reasons.

  http://cr.openjdk.java.net/~psandoz/panama/vector-abstract-class/webrev/ <http://cr.openjdk.java.net/~psandoz/panama/vector-abstract-class/webrev/>

Paul.