This allows `wgpu` to not unconditionally depend on `std::path::Path`.
It’s also, in my opinion, more user-friendly, because the feature which
most users will not use (and is not currently functional) is now a
defaultable struct field instead of a required parameter.
The disadvantage is that `wgpu-types` now has to know about tracing.
According to winit docs, pre_present_notify() should be called right
before calling present().
This actually prevents some issues on Wayland, like freezing the whole
application when the window is not visible (ask me how I know).
