Allow loading of old-style coordinate answers

[jsharkey13]

Moving to using an array means we don't load the x and y values from existing answers. This supports doing that, whilst cleaning the updated choice so that if it is submitted again there is no sign of the old-style properties.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 25 lines in your changes missing coverage. Please review.

Project coverage is 36.48%. Comparing base (fd8b29a) to head (d979d6d).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
...app/components/content/IsaacCoordinateQuestion.tsx	0.00%	25 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1287      +/-   ##
==========================================
- Coverage   36.52%   36.48%   -0.04%     
==========================================
  Files         456      456              
  Lines       19837    19855      +18     
  Branches     6503     6508       +5     
==========================================
  Hits         7245     7245              
- Misses      12554    12572      +18     
  Partials       38       38              

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