[Gradle][Minor] IdeaKotlinClasspath: Improve .toString() readability

KT-56198

libraries/tools/kotlin-gradle-plugin-idea/api/kotlin-gradle-plugin-idea.api

@@ -352,6 +352,7 @@ public final class org/jetbrains/kotlin/gradle/idea/tcs/IdeaKotlinClasspath : ja
 	public final fun size ()I
 	public fun toArray ()[Ljava/lang/Object;
 	public fun toArray ([Ljava/lang/Object;)[Ljava/lang/Object;
+	public fun toString ()Ljava/lang/String;
 }
 
 public final class org/jetbrains/kotlin/gradle/idea/tcs/IdeaKotlinClasspathKt {

libraries/tools/kotlin-gradle-plugin-idea/src/main/kotlin/org/jetbrains/kotlin/gradle/idea/tcs/IdeaKotlinClasspath.kt

@@ -73,6 +73,10 @@ class IdeaKotlinClasspath private constructor(private val files: MutableSet<File
         return files.hashCode()
     }
 
+    override fun toString(): String {
+        return "IdeaKotlinClasspath($files)"
+    }
+
     internal companion object {
         private const val serialVersionUID = 0L