Refactor `SphericalVector` interpolation method to use `array::ArrayViewVariant`.

[odlomax]

This is the last of this batch of PRs that refactors the SphericalVector interpolation method. Here we've used std::visit on ArrayViewVariant to resolve the rank and type of the arrays instead of several verbose if statements and function overloads.

This PR depends on PRs #220, #223, #224 and #226. It closes issue #217.