Replace RendererUtils.renderChild() by UIComponent.encodeAll()

Checking other issues, if was notice that RendererUtils.renderChild() is almost equal to UIComponent.encodeAll().

Historically, RendererUtils.renderChild() is older than UIComponent.encodeAll(), but the later one is better because gives the chance to the component to override it.

It is known any override goes on encodeBegin(), encodeChildren() or encodeEnd(), but to honor JSF 2.0 spec, we should fix RendererUtils.renderChildren(), and use encodeAll() instead RendererUtils.renderChild().