Completely rewritten keyword completion implementation using another approach

#KT-2816 Fixed

idea/testData/completion/keywords/InMemberFunParametersList.kt

@@ -0,0 +1,12 @@
+package TestData
+
+class TestSample() {
+    fun test(<caret>) {
+    }
+}
+
+/* TODO: they all are not correct */
+// EXIST: val
+// EXIST: var
+// EXIST: in
+// NUMBER: 3