GPUI-specific component shape runtime contracts.
This crate is also the GPUI facade for shared component-shape metadata such
as ComponentShapeMetadata, ValueChange, and McpInput.
Declare owned components with the [GpuiComponentShape] derive and external
component/state pairs with [component_shape!]. Consumer-side configured
values implement [GpuiComponentShapeBuilder] and share the
[build_component_shape] construction path with
[DefaultGpuiComponentShapeBuilder].