Add FunctionData Printing

[GabrielKS]

I implemented some more human-friendly printing of the various FunctionData:

These could be useful when I do the same thing for the PSY cost structs (NREL-Sienna/PowerSystems.jl#1048).

Also fixed a typo in existing printing test code.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.53%. Comparing base (7fe2da2) to head (5c19680).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #377      +/-   ##
==========================================
+ Coverage   77.16%   77.53%   +0.36%     
==========================================
  Files          66       66              
  Lines        5072     5092      +20     
==========================================
+ Hits         3914     3948      +34     
+ Misses       1158     1144      -14     

Flag	Coverage Δ
unittests	77.53% <100.00%> (+0.36%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
src/function_data.jl	99.40% <100.00%> (+0.08%)	⬆️

... and 1 file with indirect coverage changes

[GabrielKS]

Above formats are unchanged, added a third format that is human-readable but less verbose, for use where FunctionData are nested within other types that will convey that information (see e.g. NREL-Sienna/PowerSystems.jl#1125):

[GabrielKS]

Re-requesting review for this ^ compact addition

[kdayday]

Compact looks nice