KT-7194 No completion for member extension function inside itself

#KT-7194 Fixed

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

@@ -0,0 +1,20 @@
+class C {
+    fun String.extFun() {
+        <caret>
+    }
+
+    fun String.otherExtFun() { }
+    fun Int.wrongExtFun() { }
+
+    companion object {
+        fun String.companionExtFun() { }
+    }
+}
+
+fun String.nonMemberExtFun() {}
+
+// EXIST: extFun
+// EXIST: otherExtFun
+// ABSENT: wrongExtFun
+// EXIST: nonMemberExtFun
+// EXIST: companionExtFun