Support reflection calls to multifile class members

#KT-11447 Fixed

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KDeclarationContainerImpl.kt

@@ -39,6 +39,9 @@ internal abstract class KDeclarationContainerImpl : ClassBasedDeclarationContain
     val moduleData: RuntimeModuleData
         get() = moduleData_()
 
+    protected open val methodOwner: Class<*>
+        get() = jClass
+
     abstract val constructorDescriptors: Collection<ConstructorDescriptor>
 
     abstract fun getProperties(name: Name): Collection<PropertyDescriptor>
@@ -175,9 +178,7 @@ internal abstract class KDeclarationContainerImpl : ClassBasedDeclarationContain
     fun findMethodBySignature(name: String, desc: String, declared: Boolean): Method? {
         if (name == "<init>") return null
 
-        // Method for a top level function should be the one from the package facade.
-        // This is likely to change after the package part reform.
-        return jClass.tryGetMethod(name, loadParameterTypes(desc), declared)
+        return methodOwner.tryGetMethod(name, loadParameterTypes(desc), declared)
     }
 
     fun findDefaultMethod(name: String, desc: String, isMember: Boolean, declared: Boolean): Method? {
@@ -189,7 +190,7 @@ internal abstract class KDeclarationContainerImpl : ClassBasedDeclarationContain
         }
         addParametersAndMasks(parameterTypes, desc, false)
 
-        return jClass.tryGetMethod(name + JvmAbi.DEFAULT_PARAMS_IMPL_SUFFIX, parameterTypes, declared)
+        return methodOwner.tryGetMethod(name + JvmAbi.DEFAULT_PARAMS_IMPL_SUFFIX, parameterTypes, declared)
     }
 
     fun findConstructorBySignature(desc: String, declared: Boolean): Constructor<*>? {

core/reflection.jvm/src/kotlin/reflect/jvm/internal/KPackageImpl.kt

@@ -38,6 +38,19 @@ internal class KPackageImpl(override val jClass: Class<*>, val moduleName: Strin
         }
     }
 
+    override val methodOwner: Class<*> by lazy(LazyThreadSafetyMode.PUBLICATION) {
+        val facadeName = ReflectKotlinClass.create(jClass)?.classHeader?.multifileClassName
+        // We need to check isNotEmpty because this is the value read from the annotation which cannot be null.
+        // The default value for 'xs' is empty string, as declared in kotlin.Metadata
+        // TODO: do not read ReflectKotlinClass multiple times, obtain facade name from descriptor
+        if (facadeName != null && facadeName.isNotEmpty()) {
+            jClass.classLoader.loadClass(facadeName.replace('/', '.'))
+        }
+        else {
+            jClass
+        }
+    }
+
     internal val scope: MemberScope get() = descriptor().memberScope
 
     override val members: Collection<KCallable<*>>