[IR] Generify lowerings

#KT-1179

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt

@@ -40,6 +40,8 @@ abstract class IrClass :
 
     abstract var inlineClassRepresentation: InlineClassRepresentation<IrSimpleType>?
 
+    abstract var multiFieldValueClassRepresentation: MultiFieldValueClassRepresentation<IrSimpleType>?
+
     abstract var sealedSubclasses: List<IrClassSymbol>
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyClass.kt

@@ -17,6 +17,7 @@ import org.jetbrains.kotlin.metadata.ProtoBuf
 import org.jetbrains.kotlin.metadata.deserialization.NameResolver
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedClassDescriptor
+import org.jetbrains.kotlin.types.SimpleType
 
 class IrLazyClass(
     override val startOffset: Int,
@@ -101,9 +102,14 @@ class IrLazyClass(
     }
 
     override var inlineClassRepresentation: InlineClassRepresentation<IrSimpleType>? by lazyVar(stubGenerator.lock) {
-        descriptor.inlineClassRepresentation?.mapUnderlyingType {
-            it.toIrType() as? IrSimpleType ?: error("Inline class underlying type is not a simple type: ${render()}")
-        }
+        descriptor.inlineClassRepresentation?.mapUnderlyingType(::simplyTypeToIrOrThrow)
+    }
+
+    private fun simplyTypeToIrOrThrow(it: SimpleType) =
+        it.toIrType() as? IrSimpleType ?: error("Inline class underlying type is not a simple type: ${render()}")
+
+    override var multiFieldValueClassRepresentation: MultiFieldValueClassRepresentation<IrSimpleType>? by lazyVar(stubGenerator.lock) {
+        descriptor.multiFieldValueClassRepresentation?.mapUnderlyingType(::simplyTypeToIrOrThrow)
     }
 
     override var attributeOwnerId: IrAttributeContainer = this

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/descriptors/IrBasedDescriptors.kt

@@ -629,6 +629,9 @@ open class IrBasedClassDescriptor(owner: IrClass) : ClassDescriptor, IrBasedDecl
     override fun getInlineClassRepresentation(): InlineClassRepresentation<SimpleType>? =
         owner.inlineClassRepresentation?.mapUnderlyingType { it.toIrBasedKotlinType() as SimpleType }
 
+    override fun getMultiFieldValueClassRepresentation(): MultiFieldValueClassRepresentation<SimpleType>? =
+        owner.multiFieldValueClassRepresentation?.mapUnderlyingType { it.toIrBasedKotlinType() as SimpleType }
+
     override fun getOriginal() = this
 
     override fun isExpect() = owner.isExpect
@@ -759,6 +762,8 @@ open class IrBasedEnumEntryDescriptor(owner: IrEnumEntry) : ClassDescriptor, IrB
 
     override fun getInlineClassRepresentation(): InlineClassRepresentation<SimpleType>? = TODO("not implemented")
 
+    override fun getMultiFieldValueClassRepresentation(): MultiFieldValueClassRepresentation<SimpleType>? = TODO("not implemented")
+
     override fun getOriginal() = this
 
     override fun isExpect() = false