Add SIAMFANLEquations fixed point solvers

[ErikQQY]

Add fixed point solvers from SIAMFANLEquations.jl

Checklist

• [x] Appropriate tests were added
• [x] Any code changes were done in a way that does not break public API
• [x] All documentation related to code changes were updated
• [x] The new code follows the contributor guidelines, in particular the SciML Style Guide and COLPRAC.
• [x] Any new documentation only uses public API

Additional context

Add any other context about the problem here.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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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