Infra: Enable angle_deqp_gl46_tests on SwiftShader This change disables the WGL frontend by default on Windows when building ANGLE for desktop GL. This is because the WGL frontend is not yet fully implemented and it causes some of the trace tests to fail. The WGL frontend should be enabled by default on windows when more of its functionality gets implemented. Test: angle_deqp_gl46_tests --use-angle=swiftshader Bug: angleproject:7566 Bug: angleproject:7628 Change-Id: I69c695eb56d3858f715eeb86d28cc805e25c60eb Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3858142 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Cody Northrop <cnorthrop@google.com> Commit-Queue: Cody Northrop <cnorthrop@google.com>