Extraction refactorings: Do not suggest extraction of type elements

#KT-3994 Fixed

idea/testData/refactoring/introduceVariable/TypeElement.kt

@@ -0,0 +1,3 @@
+fun foo(t: Any) {
+    val x = t as <caret>List<String>
+}

idea/testData/refactoring/introduceVariable/TypeElement.kt.after

@@ -0,0 +1,4 @@
+fun foo(t: Any) {
+    val list = t as List<String>
+    val x = list
+}