JVM, JVM IR: report error if not all parts of multifile class are @JvmSynthetic

#KT-41884 Fixed

compiler/testData/diagnostics/testsWithJvmBackend/multifileClasses/jvmSynthetic.kt

@@ -0,0 +1,33 @@
+// WITH_RUNTIME
+// FILE: f.kt
+
+@file:JvmName("Foo")
+@file:JvmMultifileClass
+<!NOT_ALL_MULTIFILE_CLASS_PARTS_ARE_JVM_SYNTHETIC!>package test<!>
+
+fun f() {}
+
+// FILE: g.kt
+
+@file:JvmName("Foo")
+@file:JvmMultifileClass
+@file:JvmSynthetic
+package test
+
+val g = ""
+
+// FILE: h.kt
+
+@file:JvmName("Foo")
+@file:JvmMultifileClass
+<!NOT_ALL_MULTIFILE_CLASS_PARTS_ARE_JVM_SYNTHETIC!>package test<!>
+
+fun h() {}
+
+// FILE: z.kt
+
+@file:JvmName("Bar")
+@file:JvmMultifileClass
+package test
+
+fun z() {}

compiler/testData/diagnostics/testsWithJvmBackend/multifileClasses/jvmSynthetic.txt

@@ -0,0 +1,8 @@
+package
+
+package test {
+    public val g: kotlin.String = ""
+    public fun f(): kotlin.Unit
+    public fun h(): kotlin.Unit
+    public fun z(): kotlin.Unit
+}