Added Feagin Package

[ParamThakkar123]

Checklist

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

Additional context

Add any other context about the problem here.
Solves a part of #2177

[oscardssmith]

this is a mistake, right?

[ParamThakkar123]

This change was made by Chris .

[ParamThakkar123]

this is a mistake, right?

Not sure about that, really.

[ParamThakkar123]

Do we need a change here ??

[ChrisRackauckas]

I rebased this to latest master

[ParamThakkar123]

@ChrisRackauckas What are the other solvers that we are left to get done with after this ?? I will start with them simultaneously and solve the errors from here as well

[ChrisRackauckas]

Symplectic RK and Runge Kutta Nystrom (rkn) are probably next. I'll try and do the SDIRK and FIRK, and I think that would just leave Adams methods, BDF, Verner, and Explicit RK. Almost there! Thanks so much

[ParamThakkar123]

@ChrisRackauckas I started a PR for symplectic methods: #2268