RFR: 8366845: C2 SuperWord: wrong VectorCast after VectorReinterpret with swapped src/dst type

[Emanuel Peter]

I have seen 3 manifestations of this bug:

1. assert

# Internal Error (.../src/hotspot/cpu/x86/x86.ad:7640), pid=84140, tid=28419
# assert(UseAVX > 2 && VM_Version::supports_avx512dq()) failed: require


2. assert

# Internal Error (.../src/hotspot/share/opto/vectornode.cpp:1601), pid=4022154, tid=4022168
# Error: assert(bt == T_FLOAT) failed


3. Wrong result
When the feature was available but we used the wrong CastVector

It seems that [JDK-8346236](https://bugs.openjdk.org/browse/JDK-8346236) introduced reinterpret nodes to SuperWord:


  } else if (VectorNode::is_reinterpret_opcode(opc)) {
    assert(first->req() == 2 && req() == 2, "only one input expected");
    const TypeVect* vt = TypeVect::make(bt, vlen);
    vn = new VectorReinterpretNode(in1, vt, in1->bottom_type()->is_vect());


Sadly, the `src` and `dst` type are swapped. For JDK25 [JDK-8346236](https://bugs.openjdk.org/browse/JDK-8346236) this had no bad effect yet, since we only cast between HF and short, which are both based on short.

But with [JDK-8329077](https://bugs.openjdk.org/browse/JDK-8329077) we can now do reinterpret between I/F and between D/L. Here swapping has an effect, especially if it is followed by a cast:
The cast deterines its input type from the output type of the input node. If that was a reinterpret node with the wrong output type, **we would get a cast with the wrong src type**. We might do a double -> int cast instead of a long -> int cast. That leads to all sorts of issues.

The fuzzer test was only just recently added with [JDK-8324751](https://bugs.openjdk.org/browse/JDK-8324751). It uses MemorySegment, where unaligned float/double access gets handled with long/int memory access and then reinterpret (eg `MoveI2F`). But I was able to find examples that just work with `Float.intBitsToFloat` etc.

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

Commit messages:
 - fix whitespace
 - fix test vector api visibility
 - fix copyright
 - IR rules
 - JDK-8366845

Changes: https://git.openjdk.org/jdk/pull/27100/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27100&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366845
  Stats: 226 lines in 2 files changed: 225 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27100.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27100/head:pull/27100

PR: https://git.openjdk.org/jdk/pull/27100