JumpSystem cleanup

[isaacsas]

As a first step before working on making JumpSystems support coupled ODEs/SDEs, I wanted to clean up the code a bit. This

1. Adds support for collect_vars! for JumpSystems.
2. Cleans up the constructor to be more in line with how the code works for other system types. If at some point refactoring of common code in constructors is done it should now be easier to see what is different in JumpSystems.

Note that JumpSystems would still need some more work to support hierarchical modeling (i.e. sub-systems and scoping).

[isaacsas]

My plan is to next make the ArrayPartition that stores the jumps also have a component for equations, which will be used to generate an ODESystem during ODEProblem(::JumpSystem, ...) (allowing a coupled ODE-jump system).

[AayushSabharwal]

Looks good. Could you check if removing the if !(sys isa JumpSystem) here now works? It was added because collect_vars! didn't work

[isaacsas]

Will update later for that. I think we need a dispatch on the trait I added in collect_scoped_vars!.

[isaacsas]

Should be updated now.

[isaacsas]

Lots of failures here, but as far as I can tell none are related to this PR. I formatted with JuliaFormatter v1.0.62 so not sure why that is failing either. Locally it reports there is nothing to format when run on the repo.

[isaacsas]

@ChrisRackauckas I think this is good to merge now -- the test failures all seem unrelated.