[AArch64][SVE] Use SIMD variant of INSR when scalar is the result of a vector extract

At the intrinsic layer the sve.insr operation takes a scalar. When this
scalar is an integer we are forcing a data transition between GPRs and
ZPRs that is potentially costly.

Often the integer scalar is the result of a vector extract, when
performing a reduction for example. In such cases we should keep all
data within the ZPRs.

Co-authored-by: Paul Walker <paul.walker@arm.com>

Differential Revision: https://reviews.llvm.org/D101169