Add serialization/deserialization of definitely-not-null types

^KT-26245 In Progress

compiler/serialization/src/org/jetbrains/kotlin/serialization/DescriptorSerializer.kt

@@ -584,7 +584,7 @@ class DescriptorSerializer private constructor(
 
         if (type.isSuspendFunctionType) {
             val functionType = type(transformSuspendFunctionToRuntimeFunctionType(type, extension.releaseCoroutines()))
-            functionType.flags = Flags.getTypeFlags(true)
+            functionType.flags = Flags.getTypeFlags(true, false)
             return functionType
         }
 
@@ -600,6 +600,8 @@ class DescriptorSerializer private constructor(
                     builder.typeParameter = getTypeParameterId(descriptor)
                 }
 
+                builder.flags = Flags.getTypeFlags(false, type is DefinitelyNotNullType)
+
                 assert(type.arguments.isEmpty()) { "Found arguments for type constructor build on type parameter: $descriptor" }
             }
         }