Add methods for Base.complex

[odow]

Closes #3733

[araujoms]

I was going to do this now, you were too fast for me. Thanks a lot!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.40%. Comparing base (617f961) to head (7f4a302).
Report is 7 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3734      +/-   ##
==========================================
- Coverage   98.42%   98.40%   -0.02%     
==========================================
  Files          43       43              
  Lines        5825     5820       -5     
==========================================
- Hits         5733     5727       -6     
- Misses         92       93       +1     

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