Move ParsedReactionNetwork struct to Catalyst

**Is your feature request related to a problem? Please describe.** Currently, the `ParsedReactionNetwork` struct being used by both ReactionNetworkImporters.jl and SBMLImporter.jl lives in ReactionNetworkImporters.jl. Consequently, every time Catalyst does a major release SBMLImporter has to wait for ReactionNetworkImporters to update before it can update major Catalyst version. **Describe the solution you’d like** ` ParsedReactionNetwork` living in Catalyst starting from Catalyst v16. Additionally, to make import of models even smoother, it could be relevant to add functions for directly building `ODEProblem`, `SDEProblem` etc... directly from a ` ParsedReactionNetwork` . **Describe alternatives you’ve considered** The currently solution already works, I just think this could make things a bit more convenient and it would be suitable to make this change with Catalyst v16.