Use descriptors for reflection on top level properties

This also allows to obtain a Field object from the package part (see
mapping.kt)

compiler/testData/codegen/boxWithStdlib/callableReference/property/platformNamedAccessors.kt

@@ -0,0 +1,24 @@
+import kotlin.platform.platformName
+import kotlin.reflect.jvm.*
+
+var state: String = "value"
+    [platformName("getter")]
+    get
+    [platformName("setter")]
+    set
+
+fun box(): String {
+    val p = ::state
+
+    if (p.name != "state") return "Fail name: ${p.name}"
+    if (p.get() != "value") return "Fail get: ${p.get()}"
+    p.set("OK")
+
+    val getterName = p.javaGetter!!.getName()
+    if (getterName != "getter") return "Fail getter name: $getterName"
+
+    val setterName = p.javaSetter!!.getName()
+    if (setterName != "setter") return "Fail setter name: $setterName"
+
+    return p.get()
+}

compiler/testData/codegen/boxWithStdlib/reflection/mapping/topLevelProperty.kt

@@ -6,8 +6,9 @@ var topLevel = "123"
 fun box(): String {
     val p = ::topLevel
 
-    // TODO: uncomment when fields are loaded from package parts
-    // assert(p.javaField != null, "Fail p field")
+    assert(p.javaField != null, "Fail p field")
+    val field = p.javaField!!
+    assert(field.getDeclaringClass().getName() contains "_DefaultPackage\$", "Fail field not in package part: ${field.getDeclaringClass()}")
 
     val getter = p.javaGetter!!
     val setter = p.javaSetter!!