Fix default backends selection when running examples at the workspace root

[jinleili]

Connections
#2540

Description
Since wgpu-info as a workspace default-members item depends on wgpu and enabled angle vulkan-portability features, it causes #[cfg(vulkan)] #[cfg(gl)] compile conditions alway pass when run examples at the workspace root .

wgpu/wgpu-core/build.rs

Lines 10 to 19 in 9e3cd08

	vulkan: { all(not(wasm), any(windows, unix_wo_apple, feature = "vulkan-portability")) },
	metal: { all(not(wasm), apple) },
	dx12: { all(not(wasm), windows) },
	dx11: { all(not(wasm), windows) },
	gl: {
	any(
	unix_wo_apple,
	feature = "angle",
	wasm
	)

Testing
Tested examples at the workspace root and wgpu package directory

[cwfitzgerald]

I don't think this actually solves the base problem, just cures the symptoms. The problem here isn't that we are enabling the GL backend on windows, we should always be allowed to do that, the issue is that we're crashing when trying to call a function that we shouldn't be calling.

[jinleili]

@cwfitzgerald Although not solving the crash, I think what this commit solves is the inconsistent results of running the examples in the workspace root and wgpu package directory without specifying WGPU_BACKEND. The same issue exists not only on Windows, but also on macOS.

Executing cargo run --example xx from wgpu package directory on macOS, always using the metal backend

The result of executing cargo run --example xx from the workspace root on macOS.

• When no "angle" is installed, an alert window pops up:

• When vulkan is installed, always using the vk backend

[cwfitzgerald]

Mac why do you have to be like this.

Alright, I think the best option is to add a message to wgpu-info saying "for gl in non Linux add the angle feature, for vk on Mac add the vulkan-portability feature" , then remove the default features from wgpu-info, then make sure CI covers the angle and vk portability cases.

I specifically want to avoid removing wgpu-info from the default workspace.