Support properties from other modules in 'declaresDefaultValue'

Add box test using new test infra
Move serialization tests to misc compiler tests

Fixes https://github.com/Kotlin/kotlinx.serialization/issues/1602
Fixes https://github.com/Kotlin/kotlinx.serialization/issues/1481

plugins/kotlin-serialization/kotlin-serialization-compiler/testData/boxIr/multimoduleInheritance.kt

@@ -0,0 +1,56 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM_IR
+
+// WITH_RUNTIME
+
+// MODULE: lib
+// FILE: lib.kt
+
+package a
+
+import kotlinx.serialization.*
+
+@Serializable
+open class OpenBody {
+    var optional: String? = "foo"
+}
+
+@Serializable
+abstract class AbstractConstructor(var optional: String = "foo")
+
+
+// MODULE: app(lib)
+// FILE: app.kt
+
+package test
+
+import a.*
+import kotlinx.serialization.*
+import kotlinx.serialization.json.*
+import kotlin.test.assertEquals
+
+@Serializable
+class Test1: OpenBody()
+
+@Serializable
+class Test2: AbstractConstructor()
+
+fun test1() {
+    val string = Json.encodeToString(Test1.serializer(), Test1())
+    assertEquals("{}", string)
+    val reconstructed = Json.decodeFromString(Test1.serializer(), string)
+    assertEquals("foo", reconstructed.optional)
+}
+
+fun test2() {
+    val string = Json.encodeToString(Test2.serializer(), Test2())
+    assertEquals("{}", string)
+    val reconstructed = Json.decodeFromString(Test2.serializer(), string)
+    assertEquals("foo", reconstructed.optional)
+}
+
+fun box(): String {
+    test1()
+    test2()
+    return "OK"
+}