WIP: BVP Out of Place Linear problems

[n0rbed]

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
• Any new documentation only uses public API

[n0rbed]

This is made to aid the testing of SciML/SimpleBoundaryValueDiffEq.jl#13

[ErikQQY]

I think the current in-place version test cases in BVProblemLibrary.jl is fine, if you want OOP cases, you can just put them in the tests of SimpleBoundaryValueDiffEq.jl

[n0rbed]

Writing that many problems in SimpleBoundaryBVP seems overkill, plus we may need these elsewhere, so rewriting them would be bad, what do u think?

[ErikQQY]

We don’t have to test convergence on all test problems, since these are linear BVPs with analytical solutions, it’s enough as long as we can show the implemented solver have specific convergence order. I suggest you take a look at how we are doing in BoundaryValueDiffEq.jl convergence test for MIRK and FIRK methods.

[ChrisRackauckas]

It would be good to just get these here if we can. Might asw well make them reusable.

[n0rbed]

Not sure if @SVector should be used for all the OOP functions' residual or not, so only the first two problems are that way.