[DXIL] Add Float `Dot` Intrinsic Lowering (#86071)
Completes #83626
- `CGBuiltin.cpp` - modify `getDotProductIntrinsic` to be able to emit
`dot2`, `dot3`, and `dot4` intrinsics based on element count
- `IntrinsicsDirectX.td` - for floating point add `dot2`, `dot3`, and
`dot4` inntrinsics -`DXIL.td` add dxilop intrinsic lowering for `dot2`,
`dot3`, & `dot4`.
- `DXILOpLowering.cpp` - add vector arg flattening for dot product.
- `DXILOpBuilder.h` - modify `createDXILOpCall` to take a smallVector
instead of an iterator
- `DXILOpBuilder.cpp` - modify `createDXILOpCall` by moving the small
vector up to the calling function in `DXILOpLowering.cpp`.
- Moving one function up gives us access to the `CallInst` and
`Function` which were needed to distinguish the dot product intrinsics
and get the operands without using the iterator.
