Make construction of type stable TP BVProblem easier

[avik-pal]

• [x] Allow twopoint to be a Val for safer type-stability

[codecov[bot]]

Codecov Report

Merging #518 (a12a4fc) into master (75b1925) will decrease coverage by 6.84%. The diff coverage is 9.52%.

@@            Coverage Diff             @@
##           master     #518      +/-   ##
==========================================
- Coverage   53.37%   46.53%   -6.84%     
==========================================
  Files          50       50              
  Lines        3798     3823      +25     
==========================================
- Hits         2027     1779     -248     
- Misses       1771     2044     +273     

Files	Coverage Δ
src/scimlfunctions.jl	46.54% <50.00%> (-13.91%)	:arrow_down:
src/problems/bvp_problems.jl	5.88% <22.22%> (-32.05%)	:arrow_down:
src/remake.jl	44.15% <0.00%> (-9.45%)	:arrow_down:

... and 31 files with indirect coverage changes

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