Documentation for Vector API zero methods

Summary

The Vector API is missing documentation for zero methods accepting a species on IntVector and all other specializations.

Specification

Specification on DoubleVector:

/**
 * Returns a vector of the given species
 * where all lane elements are set to
 * zero, the default primitive value.
 *
 * @param species species of the desired zero vector
 * @return a zero vector
 */
public static DoubleVector zero(VectorSpecies<Double> species)

Same applies to ByteVector, ShortVector, IntVector, LongVector, and FloatVector.