Add codegen box test templates for identifiers

compiler/tests-spec/testData/codegen/box/templates/identifiers/stringTemplateElement.kt

@@ -0,0 +1,17 @@
+fun box(): String? {
+    val <!ELEMENT(1)!> = "0"
+    val <!ELEMENT(2)!> = "1"
+
+    val x1 = "${<!ELEMENT(2)!>}"
+    val x2 = "..." + "...$<!ELEMENT(1)!>..." + "..."
+    var x3 = "$<!ELEMENT(2)!>${<!ELEMENT(1)!>}$<!ELEMENT(2)!>"
+
+    if (<!ELEMENT(2)!> != "1") return null
+    if (<!ELEMENT(1)!> != "0") return null
+
+    if (x1 != "1") return null
+    if (x2 != "......0......") return null
+    if (x3 != "101") return null
+
+    return "OK"
+}