Fast Path StringCoding.countPostives and hasNegative for Power

[luke-li-2003]

Fast path the StringCoding methods countPositives and hasNegative on Power, since their logics are similar, they can be implemented by a single instrinsic.

[luke-li-2003]

Still a draft PR since I need to figure out a good way to deal with shorter arrays.

[luke-li-2003]

Related to https://github.ibm.com/runtimes/openj9-jit-xopt/issues/624

[luke-li-2003]

For reference, this is what we are dealing with:

On jdk21+:

    public static boolean hasNegatives(byte[] ba, int off, int len) {
        return countPositives(ba, off, len) != len;
    }

    @IntrinsicCandidate
    public static int countPositives(byte[] ba, int off, int len) {
        int limit = off + len;
        for (int i = off; i < limit; i++) {
            if (ba[i] < 0) {
                return i - off;
            }
        }
        return len;
    }

Before jdk21:

    public static boolean hasNegatives(byte[] ba, int off, int len) {
        for (int i = off; i < off + len; i++) {
            if (ba[i] < 0) {
                return true;
            }
        }
        return false;
    }

[luke-li-2003]

Performance: as outlined before it is not doing well for arrays shorter than byte[16]

build	byte[1]	4	8	16	30	50	100
nightly	1100	325	217	107	34	19	14
fast path	478	175	97	40	41	144	77