Initial support for KT-7090 Completion for callable references

#KT-7090 Fixed

idea/idea-completion/testData/basic/common/callableReference/EmptyQualifierInExtensionFun.kt

@@ -0,0 +1,23 @@
+class C {
+    fun memberFun(){}
+
+    val memberVal = 1
+
+    class NestedClass
+    inner class InnerClass
+
+    companion object {
+        fun companionObjectFun(){}
+    }
+}
+
+fun C.foo() {
+    val v = ::<caret>
+}
+
+// EXIST: { itemText: "memberFun", attributes: "bold" }
+// EXIST: { itemText: "memberVal", attributes: "bold" }
+// EXIST: { itemText: "hashCode", attributes: "" }
+// ABSENT: companionObjectFun
+// ABSENT: NestedClass
+// EXIST: { itemText: "InnerClass", attributes: "bold" }