Suggest assert/return postfix templates only for statements

#KT-14079 Fixed
 #KT-14090 Fixed

idea/testData/codeInsight/postfix/noReturnForNonStatement.kt

@@ -0,0 +1,3 @@
+fun foo(x: Any): Any {
+    val y = x.return<caret>
+}

idea/testData/codeInsight/postfix/noReturnForNonStatement.kt.after

@@ -0,0 +1,3 @@
+fun foo(x: Any): Any {
+    val y = x.return    <caret>
+}