KT-782 Allow backing field usage for accessors of variables on namespace level

compiler/testData/diagnostics/tests/backingField/kt782namespaceLevel.jet

@@ -0,0 +1,20 @@
+// KT-782 Allow backing field usage for accessors of variables on namespace level
+
+namespace kt782
+
+val z : Int = 34
+
+val y : Int = 11
+get() {
+    return $y
+}
+
+val x : Int
+get() = z
+
+val w : Int
+get() = <!INACCESSIBLE_BACKING_FIELD!>$z<!>
+
+fun foo() {
+    <!INACCESSIBLE_BACKING_FIELD!>$y<!> = 34
+}