More efficient code completion + fixed a few bugs

idea/testData/completion/basic/common/NoEnumEntryType.kt

@@ -0,0 +1,10 @@
+enum class E {
+    AAA
+    BBB
+
+    fun foo(): <caret>
+}
+
+// ABSENT: AAA
+// ABSENT: BBB
+

idea/testData/completion/basic/common/NoExtensionsAfterQualifier.kt

@@ -0,0 +1,9 @@
+package pack
+
+fun String.extFoo(){}
+
+fun foo() {
+    pack.<caret>
+}
+
+// ABSENT: extFoo

idea/testData/completion/basic/common/NoNestedClassAfterReceiver.kt

@@ -0,0 +1,11 @@
+class C {
+    class Nested
+    inner class Inner
+}
+
+fun foo(c: C) {
+    c.<caret>
+}
+
+// ABSENT: Nested
+// ABSENT: Inner

idea/testData/completion/basic/java/PackageDirective.kt

@@ -0,0 +1,6 @@
+package java.lang.<caret>
+
+// EXIST: annotation
+// EXIST: reflect
+// ABSENT: System
+// ABSENT: Thread