Related to #2022

Is your feature request related to a problem? Please describe.
My main render pass has a depth/stencil attachment. I'm using egui_wgpu_backend, and render pass creation assumes no depth/stencil involved.
That means, I can't render egui in my main render pass (it's incompatible with a render pipeline you create). That's unfortunate and wasteful on tiling GPU architectures.

Describe the solution you'd like
Have an Option<wgpu::TextureFormat> argument for the render pass creation, where the user would tell the format for depth/stencil, if any. It should involve minimal changes on egui wgpu side, could be done as another render pass constructor, e.g. RenderPass::with_depth_stencil.

Describe alternatives you've considered
None.

Additional context
Downstream work - kvark/vange-rs#214
Egui looks great overall, thank you for amazing work!