[FIR] Let attributes opt-in to participating in ConeClassLikeTypeImpl structural equality

This is required for EnhancedTypeForWarningAttribute because scopes
should not be reused between cone types with different values of
this attribute.

#KT-63208

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/enhancement/EnhancedTypeForWarningAttribute.kt

@@ -25,6 +25,25 @@ class EnhancedTypeForWarningAttribute(
 
     override val keepInInferredDeclarationType: Boolean
         get() = true
+
+    override val implementsEquality: Boolean
+        get() = true
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as EnhancedTypeForWarningAttribute
+
+        if (coneType != other.coneType) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        var result = coneType.hashCode()
+        return result
+    }
 }
 
 val ConeAttributes.enhancedTypeForWarning: EnhancedTypeForWarningAttribute? by ConeAttributes.attributeAccessor<EnhancedTypeForWarningAttribute>()