Move operations to compute_function style

[samtygier-stfc]

Most of our operations use the partial function style, e.g. in mantidimaging/core/operations/gaussian/gaussian.py

f = ps.create_partial(scipy_ndimage.gaussian_filter, ps.return_to_self, sigma=size, mode=mode, order=order)
...
ps.execute(f, [images.shared_array], images.data.shape[0], progress, msg="Gaussian filter")

We would like to move them to the Compute Function style e.g. in mantidimaging/core/operations/arithmetic/arithmetic.py

ps.run_compute_func(cls.compute_function, images.data.shape[0], images.shared_array, params, progress)
...
    def compute_function(i: int, array: np.ndarray, params: Dict[str, float]):
        array[i] = array[i] * (params["mult"] / params["div"]) + (params["add"] - params["sub"])

The operations_tests.py script is good for checking that the output from the change is not effected. Most operations will need some examples added to the test_cases.json.

See d703d22 for example of changing from partial to compute