Ability to force GLES-3.1 on Angle D3D11

[kvark]

Is your feature request related to a problem? Please describe.
D3D11 can easily support GLES-3.1. However, Angle is not officially conformant on this configuration.

Describe the solution you'd like
Some sort of a knob on our side that would force GLES-3.1 on Angle.
Specifically, it would add this to the context attributes:

        let mut context_attributes = vec![
            khronos_egl::CONTEXT_MAJOR_VERSION, 3,
            khronos_egl::CONTEXT_MINOR_VERSION, 1,
        ];

Describe alternatives you've considered
None

Additional context
This would make it easier to run on Windows machines that don't have proper Vulkan support. Current limitation of GLES-3.0 is way too strict there.