Add a custom trace tests loader. This custom loader will disambiguate the trace tests gl layer from the util GL/EGL loader. Bug: angleproject:4845 Change-Id: I5e8340eb50f736d931302f71f15f556fd9e52081 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2315627 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Manh Nguyen <nguyenmh@google.com>