Dispatching of analyze for parabolic terms

[andrewwinters5000]

Currently, in analysis.jl there are two versions of the analyze function. The original one (for the hyperbolic solver) dispatches only on semi::AbstractSemidiscretization. A new (experimental) version of analyze for the SemidiscretizationHyperbolicParabolic required the ability to unpack the equations_parabolic and cache_parabolic such that gradients were available to compute additional analysis quantities. In this case, the enstrophy.

The current strategy requires one to dispatch on the analysis quantity quantity::typeof(enstrophy) to avoid errors with the existing analysis quantities. This (cumbersome) way to dispatch on parabolic analysis quantities should be improved. See here for original discussion.

[DanielDoehring]

Related: #1893