[clang] [clang][clangir] add vpaddl and vpaddlq support (PR #191845)

[Andrzej Warzyński via cfe-commits]

https://github.com/banach-space commented:

Nice, thank you! 

I've left some minor comments inline. Some variants from https://arm-software.github.io/acle/neon_intrinsics/advsimd.html#pairwise-addition-and-widen are still missing - are you planning to add them in a separate PR? 

https://github.com/llvm/llvm-project/pull/191845