Refactor SDEProblem constructor

[ErikQQY]

Follow #487

Now we can define an SDEProblem by:

1. prob = SDEProblem(f, g, u0, tspan)
2. prob = SDEProblem(SDEFunction(f, g), u0, tspan) (Before we construct SDEProblem usingSDEProblem(SDEFunction(f, g), g, u0, tspan))

This PR would break a lot of downstream packages, especially the SDE stuff

[codecov]

Codecov Report

Merging #489 (cf4c46f) into master (03cdaed) will decrease coverage by 5.50%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##           master     #489      +/-   ##
==========================================
- Coverage   57.27%   51.78%   -5.50%     
==========================================
  Files          50       50              
  Lines        3703     3694       -9     
==========================================
- Hits         2121     1913     -208     
- Misses       1582     1781     +199     

Files Changed	Coverage Δ
src/problems/sde_problems.jl	33.33% <25.00%> (-22.55%)	⬇️

... and 12 files with indirect coverage changes

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[ChrisRackauckas]

I'm merging this to get it included in the v2 breaking changes. @ErikQQY can you prioritize fixing the downstream usage here a bit? I think we need to just get it done now so that way it's with the breaking change and thus everything updates appropriately.

[ErikQQY]

Sure, I am working on the downstream errors.