[cuicui_layout] integration for [bevy_sprite]

Provide the [SpriteDsl] trait, extending the [cuicui_layout]'s LayoutDsl with the following features:

• Sprite background color
• Sprite background image
• Direct spawning of text and images as argument to [spawn_ui].

Note that this is in addition to the methods LayoutDsl already supports.

Additionally, cuicui_layout_bevy_sprite provides a [ContentSized] implementation that supports Text2dBounds and Handle<Image> terminal nodes which size is determined by their content.

Check the following crates for details:

• [cuicui_layout]: the layouting algorithm
• [cuicui_dsl]: the dsl! macro and what [SpriteDsl] entails.