[FE] Make whens on expect sealed classes and enums not exhaustive

compiler/testData/codegen/box/multiplatform/exhaustiveness/commonEnum.kt

@@ -0,0 +1,29 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM
+// !LANGUAGE: +MultiPlatformProjects
+// ISSUE: KT-20306
+
+// MODULE: m1-common
+// FILE: common.kt
+enum class Base {
+    A, B
+}
+
+fun testCommon(base: Base) {
+    val x = when (base) { // must be Ok
+        Base.A -> 1
+        Base.B -> 2
+    }
+}
+
+// MODULE: m1-jvm(m1-common)
+// FILE: main.kt
+
+fun testPlatform(base: Base) {
+    val x = when (base) { // must be OK
+        Base.A -> 1
+        Base.B -> 2
+    }
+}
+
+fun box() = "OK"

compiler/testData/codegen/box/multiplatform/exhaustiveness/commonSealedClass.kt

@@ -0,0 +1,30 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM
+// !LANGUAGE: +MultiPlatformProjects
+// ISSUE: KT-44474
+
+// MODULE: m1-common
+// FILE: common.kt
+sealed class Base()
+
+class A : Base()
+object B : Base()
+
+fun testCommon(base: Base) {
+    val x = when (base) { // must be Ok
+        is A -> 1
+        B -> 2
+    }
+}
+
+// MODULE: m1-jvm(m1-common)
+// FILE: main.kt
+
+fun testPlatform(base: Base) {
+    val x = when (base) { // must be OK
+        is A -> 1
+        B -> 2
+    }
+}
+
+fun box() = "OK"

compiler/testData/codegen/box/multiplatform/exhaustiveness/commonSealedInterface.kt

@@ -0,0 +1,30 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM
+// !LANGUAGE: +MultiPlatformProjects
+// ISSUE: KT-44474
+
+// MODULE: m1-common
+// FILE: common.kt
+sealed interface Base
+
+interface A : Base
+object B : Base
+
+fun testCommon(base: Base) {
+    val x = when (base) { // must be Ok
+        is A -> 1
+        B -> 2
+    }
+}
+
+// MODULE: m1-jvm(m1-common)
+// FILE: main.kt
+
+fun testPlatform(base: Base) {
+    val x = when (base) { // must be OK
+        is A -> 1
+        B -> 2
+    }
+}
+
+fun box() = "OK"