add optional continuous_modification argument to reeval_internals_due_to_modification!

[oscardssmith]

When set to false allows the integrator to skip recalculating the interpolation data. This is a prereq to SciML/OrdinaryDiffEq.jl#2141 being finished.

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.

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (f457edc) 26.33% compared to head (3ef766a) 26.32%.

Files	Patch %	Lines
src/integrator_interface.jl	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #625      +/-   ##
==========================================
- Coverage   26.33%   26.32%   -0.02%     
==========================================
  Files          55       55              
  Lines        4249     4251       +2     
==========================================
  Hits         1119     1119              
- Misses       3130     3132       +2     

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