[SYCL][Fusion][NoSTL] Implement custom view class to replace input vector references

[jopperm]

Implement a very simple view class to transport the input vector's raw data pointers and sizes across the fusion interface, and modify FusionResult to work without std::string and std::variant.

This PR is part of a series of changes to remove uses of STL classes in the kernel fusion interface to prevent ABI issues in the future.

[sommerlukas]

Would it make sense to collect those helpers in one place (header)?

[jopperm]

You mean getView, toArrayRef and toVector, right? I think toArrayRef can't live together with the others because of the reliance of the LLVM headers. (NB: If I'm wrong and we can include those, we could just use ArrayRef directly.)

[sommerlukas]

From what I can tell, the helpers are only used in .cpp files. Could we not place them in a new header in common that is not exposed to the outside, but allows us to define the helpers in a single place and use across different source files within the JIT compiler?

As this header would be internal to the JIT compiler only, including LLVM components would not be problematic.

[jopperm]

I channeled my inner @victor-eds and found a template-based solution: View (dropped the Vector, should be specific enough as it is in the jit_compiler namespace) can now be constructed from anything that offers data() and size(), and there is a templated to method which can return any type that can be constructed from begin() and end() iterators.