Fix reflection on top level declarations from other modules

The main problem here is that moduleName that is being passed to KPackageImpl
is useless: as can be seen in
ClosureCodegen.generateCallableReferenceDeclarationContainer, the name of the
current module is always written to the class file for a callable reference,
not the name of the module of the referenced declaration. This resulted in
reflection not loading the correct .kotlin_module file and subsequently not
finding the required file facade for a top-level function.

The commit does not fix the issue with the incorrect module name written in the
back-end, but workarounds it. It turns out, reflection can figure out the name
of the module of the referenced declaration itself by parsing the header from
the given java.lang.Class object for a single-file/multi-file package facade
and extract the package_module_name protobuf extension. Similar code was
already there in Member.getKPackage() in ReflectJvmMapping.kt but it did not
support multi-file classes, of which there are a lot in the standard library;
this is now supported

 #KT-12630 Fixed
 #KT-14731 Fixed

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/header/KotlinClassHeader.kt

@@ -55,7 +55,10 @@ class KotlinClassHeader(
     }
 
     val multifileClassName: String?
-        get() = if (kind == Kind.MULTIFILE_CLASS_PART) extraString else null
+        get() = extraString.takeIf { kind == Kind.MULTIFILE_CLASS_PART }
+
+    val multifilePartNames: List<String>
+        get() = data.takeIf { kind == Kind.MULTIFILE_CLASS }?.asList().orEmpty()
 
     // TODO: use in incremental compilation
     val multifileClassKind: MultifileClassKind?