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>