[IR] Generify lowerings

#KT-1179

compiler/frontend/src/org/jetbrains/kotlin/psi/synthetics/SyntheticClassOrObjectDescriptor.kt

@@ -95,6 +95,7 @@ class SyntheticClassOrObjectDescriptor(
     override fun getUnsubstitutedMemberScope(kotlinTypeRefiner: KotlinTypeRefiner) = unsubstitutedMemberScope
     override fun getSealedSubclasses() = emptyList<ClassDescriptor>()
     override fun getInlineClassRepresentation(): InlineClassRepresentation<SimpleType>? = null
+    override fun getMultiFieldValueClassRepresentation(): MultiFieldValueClassRepresentation<SimpleType>? = null
 
     init {
         assert(modality != Modality.SEALED) { "Implement getSealedSubclasses() for this class: ${this::class.java}" }

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/descriptors/LazyClassDescriptor.java

@@ -7,6 +7,7 @@ package org.jetbrains.kotlin.resolve.lazy.descriptors;
 
 import com.intellij.psi.PsiElement;
 import com.intellij.psi.PsiNameIdentifierOwner;
+import kotlin.Pair;
 import kotlin.annotations.jvm.ReadOnly;
 import kotlin.collections.CollectionsKt;
 import kotlin.jvm.functions.Function1;
@@ -48,6 +49,7 @@ import org.jetbrains.kotlin.storage.NullableLazyValue;
 import org.jetbrains.kotlin.storage.StorageManager;
 import org.jetbrains.kotlin.types.*;
 import org.jetbrains.kotlin.types.checker.KotlinTypeRefiner;
+import org.jetbrains.kotlin.types.checker.SimpleClassicTypeSystemContext;
 
 import java.util.*;
 import java.util.stream.Collectors;
@@ -646,6 +648,28 @@ public class LazyClassDescriptor extends ClassDescriptorBase implements ClassDes
         );
     }
 
+    @Nullable
+    @Override
+    public MultiFieldValueClassRepresentation<SimpleType> getMultiFieldValueClassRepresentation() {
+        if (!InlineClassesUtilsKt.isValueClass(this) || InlineClassesUtilsKt.isInlineClass(this)) {
+            return null;
+        }
+
+        ClassConstructorDescriptor constructor = getUnsubstitutedPrimaryConstructor();
+        // Don't crash on invalid code. It is IC, not MFVC.
+        if (constructor == null) {
+            return null;
+        }
+        List<ValueParameterDescriptor> parameters = constructor.getValueParameters();
+        if (parameters.size() <= 1) {
+            return null;
+        }
+        List<Pair<Name, SimpleType>> properties = parameters.stream()
+                .map(parameter -> new Pair<>(parameter.getName(), (SimpleType) parameter.getType()))
+                .collect(Collectors.toList());
+        return new MultiFieldValueClassRepresentation<>(properties);
+    }
+
     @Override
     public String toString() {
         // not using DescriptorRenderer to preserve laziness