Generate `OpBitCast` instruction for pointer cast operation if the
element type is different.
The HLSL for the unit test is
```hlsl
StructuredBuffer<uint2> In : register(t0);
RWStructuredBuffer<double2> Out : register(u2);
[numthreads(1,1,1)]
void main() {
Out[0] = asdouble(In[0], In[1]);
}
```
Resolves https://github.com/llvm/llvm-project/issues/153513
b0ad9c293a