ST6RI-961 There can be duplicate implicit Subsettings for structurally equivalent feature chains

[adaussy]

This PR corrects a bug that results in duplicate, structurally equivalent implicit Subsetting relationships targeting feature chains.

Background

ReferenceUsageAdapter#addDefaultGeneralType() creates an implicit Subsetting from the second input parameter of a triggered TransitionUsage to:

[triggerAction, triggerPayloadParameter]

Previously, the guard in TypeAdapter#isImplicitSpecializationFor() relied on List.contains() and therefore compared the root Feature instances representing the chains. Since FeatureUtil.chainFeatures() creates a new Feature instance on every call, an existing structurally equivalent chain was not detected. Two equivalent implicit Subsettings could consequently be stored in implicitGeneralTypes.

These duplicates could later be materialized as separate relationships by TypeUtil.insertImplicitSpecializations().

Changes

Update TypeAdapter#isImplicitSpecializationFor() to structurally compare feature chains used as general types of implicit relationships.