[Trinidad] move RequestContextImpl._findRelativeComponent to public utility class

[Andrew Robinson]

The method:

static private UIComponent _findRelativeComponent(
    UIComponent from,
    String      relativeId)

on RequestContextImpl is a very handy method, any objections to making
a JIRA issue to move this to a public class with static methods?

Maybe a public static on RenderingContext? Or is there a better class?

-Andrew