Bring coord sig fig feedback in line with numeric questions

[axlewin]

• If min./max. significant figures aren't set on a coordinate question, use 2 as the default, as is the case for numeric questions.

• Coordinate questions already showed sig figs feedback in the "correct but too many sig figs" case. Add feedback for the "too few sig figs, irrespective of correctness" case if and only if we have exhausted all other relevant feedback options, as is the case for numeric questions.

• Enable significant figures feedback for both subset cases (submission ⊂ correct choice, subset match choice ⊂ submission).

[codecov]

Codecov Report

❌ Patch coverage is 77.14286% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 39.96%. Comparing base (c5f243f) to head (f54d112).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
...am/cl/dtg/isaac/quiz/IsaacCoordinateValidator.java	77.14%	3 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #761      +/-   ##
==========================================
+ Coverage   39.87%   39.96%   +0.08%     
==========================================
  Files         547      547              
  Lines       23905    23931      +26     
  Branches     2872     2880       +8     
==========================================
+ Hits         9533     9564      +31     
+ Misses      13466    13463       -3     
+ Partials      906      904       -2     

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