Moved tests

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

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

@@ -0,0 +1,10 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+tailRecursive fun Int.foo(x: Int) {
+    if (x == 0) return
+    return 1.foo(x - 1)
+}
+
+fun box(): String {
+    1.foo(1000000)
+    return "OK"
+}