[AArch64] Use the same fast math preservation for MachineCombiner...

[AArch64] Use the same fast math preservation for MachineCombiner reassociation as X86/PowerPC/RISCV. (#72820)

Don't blindly copy the original flags from the pre-reassociated
instrutions.
This copied the integer poison flags which are not safe to preserve
after reassociation.
    
For the FP flags, I think we should only keep the intersection of
the flags. Override setSpecialOperandAttr to do this.

Fixes #72777.