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.