[Gradle][MPP] Increase .toString() readability for KotlinAndroidSourceSetLayoutChecker.Diagnostic

KT-53709

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/sources/android/checker/MultiplatformLayoutV1PromoteV2Checker.kt

@@ -24,12 +24,12 @@ internal object MultiplatformLayoutV1PromoteV2Checker : KotlinAndroidSourceSetLa
         if (target.project.kotlinPropertiesProvider.ignoreMppAndroidSourceSetLayoutVersion) return
         runCatching {
             if (MultiplatformLayoutV2AgpRequirementChecker.isAgpRequirementMet()) {
-                diagnosticReporter.warning(PromoteV2LayoutDiagnostic())
+                diagnosticReporter.warning(PromoteV2LayoutDiagnostic)
             }
         }
     }
 
-    class PromoteV2LayoutDiagnostic : KotlinAndroidSourceSetLayoutChecker.Diagnostic {
+    object PromoteV2LayoutDiagnostic : KotlinAndroidSourceSetLayoutChecker.Diagnostic {
         override val message: String
             get() = """
                 ${multiplatformAndroidSourceSetLayoutV1.name} is deprecated. Use ${multiplatformAndroidSourceSetLayoutV2.name} instead. 
@@ -39,5 +39,7 @@ internal object MultiplatformLayoutV1PromoteV2Checker : KotlinAndroidSourceSetLa
                 To suppress this warning: put the following in your gradle.properties:
                 ${PropertyNames.KOTLIN_MPP_ANDROID_SOURCE_SET_LAYOUT_VERSION_1_NO_WARN}=true
             """.trimIndent()
+
+        override fun toString(): String = "PromoteV2LayoutDiagnostic"
     }
 }

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/sources/android/checker/MultiplatformLayoutV2AgpRequirementChecker.kt

@@ -28,7 +28,7 @@ internal object MultiplatformLayoutV2AgpRequirementChecker : KotlinAndroidSource
         return compareVersionNumbers(Version.ANDROID_GRADLE_PLUGIN_VERSION, AGP_VERSION_MIN) >= 0
     }
 
-    internal class AgpRequirementNotMetDiagnostic(
+    internal data class AgpRequirementNotMetDiagnostic(
         val requiredMinAgpVersion: String,
         val currentAgpVersion: String
     ) : KotlinAndroidSourceSetLayoutChecker.Diagnostic {

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/sources/android/checker/MultiplatformLayoutV2AndroidStyleSourceDirUsageChecker.kt

@@ -31,9 +31,9 @@ internal object MultiplatformLayoutV2AndroidStyleSourceDirUsageChecker : KotlinA
         }
     }
 
-    class AndroidStyleSourceDirUsageDiagnostic(
-        private val androidStyleSourceDirInUse: File,
-        private val kotlinStyleSourceDirToUse: File
+    data class AndroidStyleSourceDirUsageDiagnostic(
+        val androidStyleSourceDirInUse: File,
+        val kotlinStyleSourceDirToUse: File
     ) : KotlinAndroidSourceSetLayoutChecker.Diagnostic {
         override val message: String
             get() = """

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/plugin/sources/android/checker/MultiplatformLayoutV2MultiplatformLayoutV1StyleSourceDirUsageChecker.kt

@@ -45,7 +45,7 @@ internal object MultiplatformLayoutV2MultiplatformLayoutV1StyleSourceDirUsageChe
         }
     }
 
-    class V1StyleSourceDirUsageDiagnostic(
+    data class V1StyleSourceDirUsageDiagnostic(
         private val layout: KotlinAndroidSourceSetLayout,
         private val v1StyleSourceDirInUse: File,
         private val v2StyleSourceDirToUse: File