RFR: 8267969: Add vectorized implementation for VectorMask.eq()

[Xiaohong Gong]

Currently `"VectorMask.eq()" `is not vectorized:

    public VectorMask<E> eq(VectorMask<E> m) {
        // FIXME: Generate good code here.
        return bOp(m, (i, a, b) -> a == b);
    }

This can be implemented by calling `"xor(m.not())"` directly.

The performance improved about 1.4x ~ 1.9x for the following benchmark with different basic types:

@Benchmark
public Object eq() {
    boolean[] ma = fm.apply(size);
    boolean[] mb = fmb.apply(size);
    boolean[] mt = fmt.apply(size);
    VectorMask<Byte> m = VectorMask.fromArray(SPECIES, mt, 0);

    for (int ic = 0; ic < INVOC_COUNT; ic++) {
        for (int i = 0; i < ma.length; i += SPECIES.length()) {
            var av = SPECIES.loadMask(ma, i);
            var bv = SPECIES.loadMask(mb, i);

            // accumulate results, so JIT can't eliminate relevant computations
            m = m.and(av.eq(bv));
        }
    }

    return m;
}

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

Commit messages:
 - 8267969: Add vectorized implementation for VectorMask.eq()

Changes: https://git.openjdk.java.net/jdk/pull/4272/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4272&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267969
  Stats: 254 lines in 32 files changed: 248 ins; 6 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4272.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4272/head:pull/4272

PR: https://git.openjdk.java.net/jdk/pull/4272