GlobalISel: make truncate/extend casts uniform

They really should have both types represented, but early variants were created
before MachineInstrs could have multiple types so they're rather ambiguous.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279567 91177308-0d34-0410-b5e6-96231b3b80d8
15 files changed