RFR: JDK-8270147: Increase stride size to allow unrolling more loops

[Radoslaw Smogura]

# Description

This increase allowed stride size for loop unrolling to almost maximum possible
value which is around `max_jint /  2 - 2`,
so the value which will prevent overflow when stride is doubled in C2.

The motivation of this change is discussion and research about unrolling
vector (SIMD) loops. In such a case stride size depends on elements size
and machine size of vector for AVX256 and int stride size is 8,
and loop unroll happens. However short vectors will not cause loop unroll.


    for (int i = 0; i < SPECIES.loopBound(longSize); i += SPECIES.length() /* 8 for int, 16 for short */ ) {
      var v = ShortVector.fromByteBuffer(SPECIES, srcBufferHeap, i << 1, ByteOrder.nativeOrder());
      v.intoByteBuffer(dstBufferHeap, i << 1, ByteOrder.nativeOrder());
    }


# Notes
Stride size was decreased some time ago https://github.com/openjdk/panama-foreign/commit/2683d5390bd58683ae13bdd8582127c308d8fd04

The exact reasons for this are not known for me (over unroll of some loops?).

Original thread https://mail.openjdk.java.net/pipermail/panama-dev/2021-June/014310.html

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Commit messages:
 - Drop whitespace
 - Put back feature switch
 - Increase stride size to allow unrolling more loops

Changes: https://git.openjdk.java.net/jdk/pull/4658/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4658&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270147
  Stats: 22 lines in 2 files changed: 18 ins; 1 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4658.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4658/head:pull/4658

PR: https://git.openjdk.java.net/jdk/pull/4658