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/fir/fir-serialization/src/org/jetbrains/kotlin/fir/serialization/FirElementSerializer.kt

@@ -182,6 +182,22 @@ class FirElementSerializer private constructor(
             builder.typeTable = typeTableProto
         }
 
+        val representation = (klass as? FirRegularClass)?.getInlineClassUnderlyingParameter()
+        if (representation != null) {
+            builder.inlineClassUnderlyingPropertyName = getSimpleNameIndex(representation.name)
+
+            val property = callableMembers.single {
+                it is FirProperty && it.receiverTypeRef == null && it.name == representation.name
+            }
+            if (!property.visibility.isPublicAPI) {
+                if (useTypeTable()) {
+                    builder.inlineClassUnderlyingTypeId = typeId(representation.returnTypeRef)
+                } else {
+                    builder.setInlineClassUnderlyingType(typeProto(representation.returnTypeRef))
+                }
+            }
+        }
+
         if (versionRequirementTable == null) error("Version requirements must be serialized for classes: ${klass.render()}")
 
         builder.addAllVersionRequirement(versionRequirementTable.serializeVersionRequirements(klass))