Does wgpu_hal::dx12 properly recognize added and removed adapters?

[jimblandy]

In Direct3D 12, it seems that the system is scanned for available adapters only when you create an IDXGIFactory (docs):

When you create a factory, the factory enumerates the set of adapters that are available in the system. Therefore, if you change the adapters in a system, you must destroy and recreate the IDXGIFactory object. The number of adapters in a system changes when you add or remove a display card, or dock or undock a laptop.

wgpu_hal::dx12::Instance::factory is the IDXGIFactory that we use for all enumeration. This implies that if wgpu_core wants to see new devices or be informed of devices going away, it needs to create an entirely new Api::Instance, which is not generally the way we expect to use the wgpu_hal API.

I'm not a Windows dev, but it seems to me that we should probably be creating a fresh IDXGIFactory every time we call wgpu_hal::Instance::enumerate_adaptors.