Do not try to generate 'expect' declarations in multifile classes

Similarly to PackageCodegenImpl#generateFile

 #KT-15754 Fixed
 #KT-17478 Fixed

compiler/testData/multiplatform/jvmMultifileClass/common.kt

@@ -0,0 +1,6 @@
+// WITH_RUNTIME
+
+@file:kotlin.jvm.JvmMultifileClass
+@file:kotlin.jvm.JvmName("CommonKt")
+
+expect fun foo()

compiler/testData/multiplatform/jvmMultifileClass/jvm.kt

@@ -0,0 +1,5 @@
+actual fun foo() {}
+
+fun test() {
+    foo()
+}

compiler/testData/multiplatform/jvmMultifileClass/output.txt

@@ -0,0 +1,7 @@
+-- Common --
+Exit code: OK
+Output:
+
+-- JVM --
+Exit code: OK
+Output: