Use conditional logic to select the error message for an unmatched identifier based on whether it was a case-insensitive match

[lukedegruchy]

Closes #598

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 64.32432% with 66 lines in your changes missing coverage. Please review.

Project coverage is 63.73%. Comparing base (100ebe3) to head (8cd2d2e).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...va/org/cqframework/cql/cql2elm/LibraryBuilder.java	71.17%	23 Missing and 9 partials ⚠️
...k/cql/cql2elm/model/ResolvedIdentifierContext.java	41.81%	30 Missing and 2 partials ⚠️
...cqframework/cql/cql2elm/model/CompiledLibrary.java	89.47%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1406      +/-   ##
============================================
- Coverage     63.74%   63.73%   -0.02%     
  Complexity     2666     2666              
============================================
  Files           493      494       +1     
  Lines         27782    27834      +52     
  Branches       5523     5527       +4     
============================================
+ Hits          17711    17741      +30     
- Misses         7828     7850      +22     
  Partials       2243     2243              

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