Better code generation for toString() on primitives

When using .toString() on a primitive Xtend generates BoxedPrimitive.valueOf(a).toString() instead of BoxedPrimitive.toString(a).

For example, the following Xtend:

private def void doThing() {
	val int a = 0;
	val String b = a.toString
}

Generates the following Java:

private void doThing() {
	final int a = 0;
	final String b = Integer.valueOf(a).toString(); // Should use Integer.toString(a)
}

This allocates a boxed primitive while a static function is available exactly for this purpose.

Start by locating the Xtend code-generation entry point for primitive .toString() calls and reproduce the issue with the example in this report. Done means the generated Java uses the primitive wrapper's static toString(a) method instead of boxing through valueOf(a).toString().