refactor(model): Serialize dependency graph edges in sorted order

Improve human readability and make the serialized ordering independent
from the insertion order.

Signed-off-by: Frank Viernau <frank_viernau@epam.com>

model/src/main/kotlin/DependencyGraph.kt

@@ -21,9 +21,11 @@ package org.ossreviewtoolkit.model
 
 import com.fasterxml.jackson.annotation.JsonIgnore
 import com.fasterxml.jackson.annotation.JsonInclude
+import com.fasterxml.jackson.databind.annotation.JsonSerialize
 
 import java.util.SortedSet
 
+import org.ossreviewtoolkit.model.utils.DependencyGraphEdgeSortedSetConverter
 import org.ossreviewtoolkit.model.utils.PackageLinkageValueFilter
 
 /**
@@ -102,6 +104,7 @@ data class DependencyGraph(
      * A set with the edges of this dependency graph. By traversing the edges, the dependencies of packages can be
      * determined.
      */
+    @JsonSerialize(converter = DependencyGraphEdgeSortedSetConverter::class)
     val edges: Set<DependencyGraphEdge>? = null
 ) {
     companion object {

model/src/main/kotlin/utils/SortedSetConverters.kt

@@ -27,6 +27,7 @@ import java.util.SortedSet
 
 import org.ossreviewtoolkit.model.ArtifactProvenance
 import org.ossreviewtoolkit.model.CopyrightFinding
+import org.ossreviewtoolkit.model.DependencyGraphEdge
 import org.ossreviewtoolkit.model.FileList
 import org.ossreviewtoolkit.model.Identifier
 import org.ossreviewtoolkit.model.LicenseFinding
@@ -44,6 +45,10 @@ class CopyrightFindingSortedSetConverter : StdConverter<Set<CopyrightFinding>, S
     override fun convert(value: Set<CopyrightFinding>) = value.toSortedSet(CopyrightFinding.COMPARATOR)
 }
 
+class DependencyGraphEdgeSortedSetConverter : StdConverter<Set<DependencyGraphEdge>, Set<DependencyGraphEdge>>() {
+    override fun convert(value: Set<DependencyGraphEdge>) = value.toSortedSet(compareBy({ it.from }, { it.to }))
+}
+
 /** Do not convert to SortedSet in order to not require a comparator consistent with equals */
 class FileListSortedSetConverter : StdConverter<Set<FileList>, Set<FileList>>() {
     override fun convert(value: Set<FileList>) = value.sortedBy { it.provenance.getSortKey() }.toSet()