RFR: 8260355: AArch64: deoptimization stub should save vector registers [v4]

[Vladimir Ivanov]

>> I've also previously run the tier1 and java/incubator/vector/* tests
>> with -XX:+DeoptimizeALot. My experience of modifying that code is that
>> DeoptimizeALot fails pretty quickly if you get something wrong.
> 
> Yeah. The problem here is that safepoints with live vectors aren't so
> common, so it's hard to test, I get it. Maybe this will have to do.

FTR jdk/java/incubator/vector tests w/ -XX:+DeoptimizeALot are very good 
at verifying that in-register vector values are properly preserved: 
vectors (as exposed by Vector API) are routinely kept in registers 
across safepoints and during deoptimization they are rematerialized into 
full-blown Vector instances, so the tests fail quickly on broken vector 
values.

Best regards,
Vladimir Ivanov