Allow subset matching for coordinate questions

[axlewin]

In the coordinate question validator:

(1) If a submission is a proper subset of a correct choice, display feedback to indicate this.

(2) If a choice with allowSubsetMatch is a proper subset of a submission, match the choice (assuming that no strict choices matched).

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 38.29%. Comparing base (4411e40) to head (6b0e884).
⚠️ Report is 54 commits behind head on main.

Files with missing lines	Patch %	Lines
...am/cl/dtg/isaac/quiz/IsaacCoordinateValidator.java	75.00%	9 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #750      +/-   ##
==========================================
+ Coverage   36.77%   38.29%   +1.52%     
==========================================
  Files         545      541       -4     
  Lines       23692    23688       -4     
  Branches     2832     2831       -1     
==========================================
+ Hits         8712     9072     +360     
+ Misses      14102    13735     -367     
- Partials      878      881       +3     

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