Regression in LoopOverNonConstantFP

The LoopOverNonConstantFP benchmark shows some regression:

```
Benchmark Mode Cnt Score Error Units
LoopOverNonConstantFP.BB_loop avgt 30 0.527 ? 0.014 ms/op
LoopOverNonConstantFP.segment_loop avgt 30 14.853 ? 0.137 ms/op
LoopOverNonConstantFP.unsafe_loop avgt 30 0.529 ? 0.011 ms/op
```

Looking more closely, the issue seems to be triggered by an inexat var handle call:

```
java.lang.invoke.WrongMethodTypeException: handle's method type (MemorySegment,long,double)void but found (AbstractMemorySegmentImpl,long,double)void
```

This was introduced when all default methods in MemorySegment were moved to AbstractMemorySegmentImpl