ARM64 SVE: Zip/Unzip should use predicate variant when all inputs are masks

[a74nh]

See #101294 (review)

There is a version of zip/unzip that takes predicates as inputs and output.

In lowering (?) we should check the inputs, if they are all convert-from-masks then we should remove the masks and then in codegen detect somehow (how if the masks have been removed? maybe we contain the mask conversions??)

By itself this is a low priority optimisation, but we should do it as soon as other instructions will also probably fit the same pattern. (Add them to this ticket as we find them)

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[tannergooding]

In lowering (?) we should check the inputs, if they are all convert-from-masks then we should remove the masks and then in codegen detect somehow (how if the masks have been removed? maybe we contain the mask conversions??)

We notably do this in morph for x64 to catch various early cases, but rechecking in lowering may be able to catch others as well.