Use SubsetReplace for Symbolic implementation

[maxitg]

The problem

Wolfram Language (Method -> "Symbolic") implementation is currently quite complex and inefficient. Since it was introduced, however, a new Wolfram Language version was released, which now has SubsetReplace. It's more efficient than the current implementation, supports arbitrary WL patterns, and we should use it in the symbolic implementation.

Note, that it is not sufficient to simply use SubsetReplace instead of, say, WolframModel because WolframModel offers more evolution options (such as step limits based on different properties of the states), and analysis tools (such as causal graphs).

Possible solution

Using SubsetReplace should eliminate the need for toNormalRules, however, incorporating it is not as simple as calling it in setReplace$wl because we still need to care about evolution order. SubsetReplace does not offer many options to control evolution, and we will need to find a way around that.

Alternative solutions

We could also modify the C++ implementation to call back Wolfram Kernel and support arbitrary expressions. That would eliminate a lot of code duplication. However, that is also non-trivial to do, and having two independent implementations is useful for testing.