[WGPU] Allow for depth buffer in web target (#2335)

* Add depth stencil initialization to `Painter`

* Move depth stencil initialization into `resize_and_generate_depth_texture_view`, and call it in `set_window` and `on_window_resized`

* Allow for depth texture in WASM builds

* change `map` to `if let` statement

* use reference for render state

* Clean up descriptors and move texture generation to on resize events

* remove unused field from WebOptions

crates/egui-wgpu/src/lib.rs

@@ -55,6 +55,8 @@ pub struct WgpuConfiguration {
 
     /// Callback for surface errors.
     pub on_surface_error: Arc<dyn Fn(wgpu::SurfaceError) -> SurfaceErrorAction>,
+
+    pub depth_format: Option<wgpu::TextureFormat>,
 }
 
 impl Default for WgpuConfiguration {
@@ -68,6 +70,7 @@ impl Default for WgpuConfiguration {
             backends: wgpu::Backends::PRIMARY | wgpu::Backends::GL,
             present_mode: wgpu::PresentMode::AutoVsync,
             power_preference: wgpu::PowerPreference::HighPerformance,
+            depth_format: None,
 
             on_surface_error: Arc::new(|err| {
                 if err == wgpu::SurfaceError::Outdated {