skia: fire RenderingSetup for the WGPU-backed renderers

SkiaWGPURendererGeneric::new_with_surface built its SkiaRenderer via
SkiaRenderer::default(), the constructor for a surface that arrives
later through a window handle. This renderer already owns its surface at
construction, so rendering_first_time never got set and neither
RenderingSetup nor RenderingTeardown was never delivered to the
rendering notifier.

Route through SkiaRenderer::new_with_surface instead, the constructor
for an eagerly-attached surface. WGPUSurface gains a Surface::as_any
override so render_to_texture can still reach its concrete fields
after handing the surface to SkiaRenderer's ownership.

ChangeLog: Fixed SkiaWGPU29Renderer/SkiaWGPU30Renderer never firing RenderingState::RenderingSetup/RenderingTeardown