Make ResourceDevice actually generic over the backend

[lukaslihotzki]

The ResourceDevice trait is intended not to depend on the specific backend. This is shown by the type parameters that are used in the function signatures (such as Self::Texture) instead of super::Texture. However, super::TextureViewDesc contains super::Texture, so the trait indirectly depends on the concrete super::Texture, but not on all the other type parameters. Therefore, this seems like an oversight.

To fix this inconsistency, this PR makes crate::TextureViewDesc generic over the contained Texture, so the trait can use this struct with the correct Self::Texture type parameter. Advantage of this solution is that users don't need to change the code if they just pass the TextureViewDesc to create_texture_view, even if there were different implementations of ResourceDevice. Alternative solution would be to exclude the actual Texture from TextureViewDesc and just specify it as first parameter in create_texture_view. Another solution would be to add a Self::TextureViewDesc type parameter to ResourceDevice, but then, it would be difficult for users to create the TextureViewDesc in a generic way.

I would be happy if this inconsistency is fixed with any solution (the mentioned ones or another).

[lukaslihotzki]

This change is related to #148, but it makes sense on its own.

[kvark]

Thank you!