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/parAfterUserType.kt

@@ -0,0 +1,5 @@
+class A
+fun foo(a: Any) {
+    // Do not suggest 'A' as an expression to parenthesize
+    a as A.par<caret>
+}

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

@@ -0,0 +1,5 @@
+class A
+fun foo(a: Any) {
+    // Do not suggest 'A' as an expression to parenthesize
+    (a as A)
+}

idea/testData/codeInsight/postfix/valAfterReceiver.kt

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

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

@@ -0,0 +1,7 @@
+class A {
+    fun bar() = 1
+}
+fun foo(a: A) {
+    val a1 = a
+    val x = a1.bar()
+}

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>
+}

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

@@ -0,0 +1,7 @@
+class A {
+    fun bar() = 1
+}
+fun foo(a: A) {
+    val bar = a.bar()
+    val x = bar
+}