Add filtering of suggested expressions for postfix templates

Do not suggest qualified expression's selector or a part of user type
because they aren't really independent expressions

idea/testData/codeInsight/postfix/valAfterSelector.kt

@@ -0,0 +1,6 @@
+class A {
+    fun bar() = 1
+}
+fun foo(a: A) {
+    val x = a.bar().val<caret>
+}