KT-7194 No completion for member extension function inside itself

#KT-7194 Fixed

idea/testData/completion/basic/common/extensions/NoMemberExtensionsFromCompanionObject.kt

@@ -0,0 +1,14 @@
+class C {
+    fun String.extFun() { }
+
+    companion object {
+        fun String.foo() {
+            <caret>
+        }
+    }
+}
+
+fun String.nonMemberExtFun() {}
+
+// EXIST: nonMemberExtFun
+// ABSENT: extFun