Code completion: do not list instance members from context with no instance

#KT-6388 Fixed
 #KT-4422 Fixed
 #KT-5516 Fixed

idea/testData/completion/basic/multifile/NoExtForOuterFromNested/NoExtForOuterFromNested.dependency.kt

@@ -0,0 +1,6 @@
+package second
+
+import first.OuterClass
+
+fun OuterClass.outerExtension() {
+}

idea/testData/completion/basic/multifile/NoExtForOuterFromNested/NoExtForOuterFromNested.kt

@@ -0,0 +1,12 @@
+package first
+
+class OuterClass {
+    class Nested {
+        fun foo() {
+            out<caret>
+        }
+    }
+}
+
+// INVOCATION_COUNT: 2
+// ABSENT: outerExtension