Moved tests

that are used both for codegen & diagnostics to codegen/box/diagnostics

compiler/testData/codegen/box/diagnostics/functions/tailRecursion/realStringRepeat.kt

@@ -0,0 +1,8 @@
+tailRecursive fun String.repeat(num : Int, acc : StringBuilder = StringBuilder()) : String =
+        if (num == 0) acc.toString()
+        else repeat(num - 1, acc.append(this))
+
+fun box() : String {
+    val s = "a".repeat(10000)
+    return if (s.length == 10000) "OK" else "FAIL: ${s.length}"
+}