Check return type of internal @PublishedApi functions in Explicit API mode

#KT-38981 Fixed

compiler/testData/diagnostics/testsWithExplicitApi/publishedApi.kt

@@ -0,0 +1,7 @@
+// SKIP_TXT
+// WITH_RUNTIME
+
+public class A {
+    @PublishedApi
+    internal fun <!NO_EXPLICIT_RETURN_TYPE_IN_API_MODE!>foo<!>() = 1
+}