Add SIAMFANLEquations fixed point solvers

[ErikQQY]

Add fixed point solvers from SIAMFANLEquations.jl

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

All modified and coverable lines are covered by tests ✅

Comparison is base (e722fad) 88.02% compared to head (a72da25) 88.06%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #344      +/-   ##
==========================================
+ Coverage   88.02%   88.06%   +0.03%     
==========================================
  Files          28       28              
  Lines        2172     2178       +6     
==========================================
+ Hits         1912     1918       +6     
  Misses        260      260              

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