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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[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

@@ Coverage Diff @@## master #493 +/- ##
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Coverage 73.51% 73.51% =======================================
Files 451 451 Lines 37692 37692 Branches 5183 5183 =======================================
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.