[SVE][CodeGen] Lower scalable masked scatters
Lowers the llvm.masked.scatter intrinsics (scalar plus vector addressing mode only)
Changes included in this patch:
- Custom lowering for MSCATTER, which chooses the appropriate scatter store opcode to use. Floating-point scatters are cast to integer, with patterns added to match FP reinterpret_casts.
- Added the getCanonicalIndexType function to convert redundant addressing modes (e.g. scaling is redundant when accessing bytes)
- Tests with 32 & 64-bit scaled & unscaled offsets
Reviewed By: sdesmalen
Differential Revision: https://reviews.llvm.org/D90941