Limit compiled backends

We probably do not want to build all backends.

Limiting it to: 
Windows: d3d9 and d3d11
Macos: metal
Linux: Vulkan?

We can also safely disable
- angle_enable_null "null display types which perform state tracking and validation but do not render any content."
- angle_enable_gl "Desktop GL"

https://github.com/google/angle/blob/main/doc/DevSetup.md#choosing-a-backend