Small fixes after review: do not set is_pure=true for named constants refactoring

compiler/testData/evaluate/isPure/enum.kt

@@ -2,7 +2,7 @@ package test
 
 enum class MyEnum { A }
 
-// val prop1: true
+// val prop1: null
 val prop1 = MyEnum.A
 
 // val prop2: null

compiler/testData/evaluate/isPure/namedConstants.kt

@@ -0,0 +1,9 @@
+package test
+
+val NAMED_CONSTANT = 1
+
+// val prop1: null
+val prop1 = NAMED_CONSTANT
+
+// val prop2: null
+val prop2 = NAMED_CONSTANT + 1