[AArch64][GlobalISel] Emit G_ASSERT_SEXT for SExt parameters in CallLowering

Similar to how we emit G_ASSERT_ZEXT when we have CCValAssign::LocInfo::ZExt.

This will allow us to combine away some redundant sign extends.

Example: https://godbolt.org/z/cTbKvr

Differential Revision: https://reviews.llvm.org/D96915