Add symmetric coloring function

Motivation

Hessian coloring is slightly different from Jacobian coloring, so it needs a dedicated function symmetric_coloring, which this PR introduces.

Now we have all we need to implement problems P1 and P2 of the reference paper What color is your Jacobian? (see tables below). The actual coloring algorithm will vary between column_coloring/row_coloring and symmetric_coloring, but that's okay: we can subtype AbstractColoringAlgorithm as follows

struct GreedyColoringAlgorithm <: AbstractColoringAlgorithm
    vertex_ordering_function::Function  # for instance largest degree first
end

and then dispatch

column_coloring(M, ::GreedyColoringAlgorithm) = # greedy distance-2 coloring
row_coloring(M, ::GreedyColoringAlgorithm) = # greedy distance-2 coloring
symmetric_coloring(M, ::GreedyColoringAlgorithm) = # greedy star coloring

Checklist

[x] Appropriate tests were added
[x] Any code changes were done in a way that does not break public API
[x] All documentation related to code changes were updated
[x] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
[x] Any new documentation only uses public API

SciML / ADTypes.jl

Add symmetric coloring function #43

Motivation

Checklist

Codecov Report