[SVE][CodeGen] Lower scalable integer vector reductions

This patch uses the existing LowerFixedLengthReductionToSVE function to also lower
scalable vector reductions. A separate function has been added to lower VECREDUCE_AND
& VECREDUCE_OR operations with predicate types using ptest.

Lowering scalable floating-point reductions will be addressed in a follow up patch,
for now these will hit the assertion added to expandVecReduce() in TargetLowering.

Reviewed By: paulwalker-arm

Differential Revision: https://reviews.llvm.org/D89382