[AA] Add toString implementation for KtLibraryModuleImpl

- This allows stable mentions of test module libraries in output test
  data.

^KT-56288

analysis/analysis-test-framework/tests/org/jetbrains/kotlin/analysis/test/framework/project/structure/KtLibraryModuleImpl.kt

@@ -27,4 +27,6 @@ class KtLibraryModuleImpl(
     override val directRegularDependencies: MutableList<KtModule> = mutableListOf()
     override val directDependsOnDependencies: MutableList<KtModule> = mutableListOf()
     override val directFriendDependencies: MutableList<KtModule> = mutableListOf()
-}
+
+    override fun toString(): String = libraryName
+}