[DirectX] Add test Support typedBufferLoad and Store for RWBuffer<int64_t2>, RWBuffer<uint64_t2>

[spall]

HLSL's Buffer/RWBuffer can operate on a vector of two 64 bit integers, like so: https://hlsl.godbolt.org/z/Mevonvav8

The typedBufferLoad and Store dxil intrinsics (introduced in llvm/llvm-project#104252 and llvm/llvm-project#104253) should be taught to handle a vector of 2 64 bit integers.

Support needs to be added for int64_t and uint64_t as well.

[damyanp]

Doing this should fix llvm/llvm-project#140321.

We need to add a test to the offload test suite for this.