IR: add IrClass.getInlineClassRepresentation, serialize/deserialize it

The change in FirDeclarationUtil is needed because in case of unsigned
types loaded from the standard library, the primary constructor for some
reason is not the first, but the second in the list of constructors.

compiler/ir/ir.tree.impl/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt

@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
+import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.name.Name
 
@@ -64,6 +65,8 @@ class IrClassImpl(
 
     override var superTypes: List<IrType> = emptyList()
 
+    override var inlineClassRepresentation: InlineClassRepresentation<IrSimpleType>? = null
+
     override var metadata: MetadataSource? = null
 
     override var attributeOwnerId: IrAttributeContainer = this