create StringValue only for primitive compile time values

compiler/testData/evaluate/strings.kt

@@ -0,0 +1,26 @@
+package test
+
+enum class MyEnum {
+    A
+}
+
+// val prop1: "2"
+val prop1 = "${1 + 1}"
+
+// val prop2: null
+val prop2 = "myEnum=${MyEnum.A}"
+
+// val prop3: "1"
+val prop3 = "${1}"
+
+// val prop4: null
+val prop4 = "${null}"
+
+// val prop5: "1.0"
+val prop5 = "${1.toFloat()}"
+
+// val prop6: "1.0"
+val prop6 = "${1.0}"
+
+// val prop7: null
+val prop7 = "${javaClass<Int>()}"