Check subrange liveness at rematerialization

LiveRangeEdit::allUsesAvailableAt checks that VNI at use is the same
as at the original use slot. However, the VNI can be the same while
a specific subrange needed for use can be dead at the new index.

This patch adds subrange liveness check if there is a subreg use.

Fixes: SWDEV-312810

Differential Revision: https://reviews.llvm.org/D115278