Overhaul the entire element system

Now the Element trait is designed to be wrapped in a Lifecycle enum that gets placed inside an ElementBox. This allows the framework to store data on behalf of the Element implementation, such as sizes, bounds, and also implementation-specific LayoutState and PaintState types. This makes it easier to reason about which data is available in each Element method.

gpui/src/platform/mac/renderer.rs

@@ -97,7 +97,6 @@ impl Renderer {
         for quad_batch in layer.quads().chunks(batch_size) {
             for (ix, quad) in quad_batch.iter().enumerate() {
                 let bounds = quad.bounds * scene.scale_factor();
-                log::info!("render quad {:?}", quad);
                 let shader_quad = shaders::GPUIQuad {
                     origin: bounds.origin().to_float2(),
                     size: bounds.size().to_float2(),