824: make all labels use `wgpu::Label` r=kvark a=LU15W1R7H
This PR does a very minor change.
It replaces all occurences of `label: Option<'a str>` with `label: crate::Label`,
making the usage consistent all across the API.
This doesn't bring any benefit other than consistency.
I hope to have catched every occurance.
Co-authored-by: Luis Wirth <lwirth2000@gmail.com>