Fix bug in MergeEquivalentAnalyses

[jtmaxwell3]

Comparing MergeEquivalentAnalyses to John Lambert's memoization code, I noticed that it was not computing equivalence correctly. So I borrowed AnalysisStateKey from the memoization code to fix the problem.

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This change is 

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 73.51%. Comparing base (d734722) to head (4562502).

Additional details and impacted files

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##           master     #493   +/-   ##
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  Coverage   73.51%   73.51%           
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  Files         451      451           
  Lines       37692    37692           
  Branches     5183     5183           
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  Hits        27708    27708           
  Misses       8845     8845           
  Partials     1139     1139           

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[ddaspit]

@ddaspit reviewed 1 file and all commit messages, and made 1 comment.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on jtmaxwell3).

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src/SIL.Machine.Morphology.HermitCrab/AnalysisStratumRule.cs line 155 at r1 (raw file):

                if (mergeEquivalentAnalyses)
                {
                    var key = AnalysisStateKey.PinAndKey(mruleOutWord);

wordCache and output don't agree on identity. Word.ValueEquals ignores SyntacticFeatureStruct, which the key includes. So analyses differing only in SyntacticFeatureStruct now get distinct keys, skip the merge, and are then dropped by output.Add.

Also, wordCache[key] = mruleOutWord runs before output.Add accepts it, so a rejected word stays canonical and swallows every later word with that key.