Make DifferentiateWith compatible with ForwardDiff, clarify docs

[gdalle]

DIT source

• Clarify documentation of DifferentiateWith, mention compositions.

DIT extensions

• Make DifferentiateWith compatible with ForwardDiff through Dual and AbstractArray{<:Dual} overloads

DI tests

• Test DifferentiateWith for Zygote and ForwardDiff on the closurified backends, using FiniteDiff as substitute

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.84%. Comparing base (5750b31) to head (604e067).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #487      +/-   ##
==========================================
- Coverage   98.51%   97.84%   -0.67%     
==========================================
  Files         107      107              
  Lines        4298     4311      +13     
==========================================
- Hits         4234     4218      -16     
- Misses         64       93      +29     

Flag	Coverage Δ
DI	98.31% <100.00%> (-0.27%)	⬇️
DIT	96.88% <ø> (-1.49%)	⬇️

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