Data flow values: more accurate handling of postfix ++ and --

compiler/testData/diagnostics/tests/smartCasts/varnotnull/plusplusMinusminus.kt

@@ -0,0 +1,20 @@
+fun foo(arg: Int?): Int {
+    var i = arg
+    if (i != null && <!DEBUG_INFO_SMARTCAST!>i<!>++ == 5) {
+        return <!DEBUG_INFO_SMARTCAST!><!DEBUG_INFO_SMARTCAST!>i<!>--<!> + <!DEBUG_INFO_SMARTCAST!>i<!>
+    }
+    return 0
+}
+
+operator fun Long?.inc() = this?.let { it + 1 }
+
+fun bar(arg: Long?): Long {
+    var i = arg
+    if (i++ == 5L) {
+        return i<!UNSAFE_CALL!>--<!> <!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>+<!> i
+    }
+    if (i++ == 7L) {
+        return i++ <!NONE_APPLICABLE!>+<!> i
+    }
+    return 0L
+}

compiler/testData/diagnostics/tests/smartCasts/varnotnull/plusplusMinusminus.txt

@@ -0,0 +1,5 @@
+package
+
+public fun bar(/*0*/ arg: kotlin.Long?): kotlin.Long
+public fun foo(/*0*/ arg: kotlin.Int?): kotlin.Int
+public operator fun kotlin.Long?.inc(): kotlin.Long?