JVM_IR. Support runtime string concatenation

compiler/testData/codegen/bytecodeText/stringOperations/concatDynamic.kt

@@ -2,12 +2,15 @@
 // JVM_TARGET: 9
 class A
 
+inline class IC(val x: String)
+
 inline fun test(s: (String) -> Unit) {
     s("456")
 }
 
-fun box(a: String, b: String?) {
-    val s = a + "1" + "2" + 3 + 4L + b + 5.0 + 6F + '7' + A() + true + false + 1u
+fun box(a: String, b: String?, x: IC?) {
+    val p = 3147483648u
+    val s = a + "1" + "2" + 3 + 4L + b + 5.0 + 6F + '7' + A() + true + false + 3147483647u + p + x
 
     a.plus(b)
     b?.plus(a)
@@ -17,9 +20,27 @@ fun box(a: String, b: String?) {
     test("123"::plus)
 }
 
-// unsigned constant 1u processed as argument (last \u0001)
-
-// 1 "\\u00011234\\u00015.06.07\\u0001truefalse\\u0001"
-// 6 INVOKEDYNAMIC makeConcatWithConstants
+// 7 INVOKEDYNAMIC makeConcatWithConstants
+// 1 "IC\(x=\\u0001\)"
 // 0 append
-// 0 stringPlus
+// 0 stringPlus
+
+// JVM_TEMPLATES
+// unsigned constant 3147483647u is processed as argument (\u0001) and it adds additional `UInt.toString-impl` call
+// 1 "\\u00011234\\u00015.06.07\\u0001truefalse\\u0001\\u0001\\u0001"
+// 2 INVOKESTATIC kotlin/UInt.toString-impl
+
+// Old backend perform inline class boxing...
+// 1 INVOKESTATIC IC.box-impl
+
+// one in IC.toString()
+// 1 INVOKESTATIC IC.toString-impl
+
+// JVM_IR_TEMPLATES
+//  unsigned constant 3147483647u is inlined
+// 1 "\\u00011234\\u00015.06.07\\u0001truefalse3147483647\\u0001\\u0001"
+// 1 INVOKESTATIC kotlin/UInt.toString-impl
+
+// .. but ir backend performs wise `toString-impl` call
+// one in IC.toString() + one in concatenation
+// 2 INVOKESTATIC IC.toString-impl