The Khronos conformance tests only test configs that have the conformant
bit set. ANGLE is currently targetting OpenGL ES 2.0 conformance, so this
change is setting the EGL_OPENGL_ES2_BIT bit to indicate this.

ES 2.0 conformance reporting is being restricted by
ANGLE_VULKAN_CONFORMANT_CONFIGS_ONLY for official builds, but ES 3.0
conformance will be reported for builds without
ANGLE_VULKAN_CONFORMANT_CONFIGS_ONLY enabled.

Bug: angleproject:3374
Test: CQ Dry Run
Change-Id: Ie31f63c3ea3b7bddfceec80ebc28f079ffd363df
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1564717Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Tim Van Patten <timvp@google.com>