Add a feature flag allowES3OnFL10_0 to allow ES3 on d3d10.0. (Originally by Jeff Muizelaar <jrmuizel@gmail.com>) This lets us run WebRender on devices that only support D3D 10.0. Firefox bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1620075 Bug: angleproject:6189 Change-Id: I77c09851c50dee206702b1da25a9ef0c05eeb6c6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3036598 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jeff Gilbert <jgilbert@mozilla.com>