[cuicui_layout] integration for [bevy_ui]

Provides the [UiDsl] trait, extending the [cuicui_layout]'s LayoutDsl with the following features:

• Style border color and width (but only uniform)
• UI node background color
• UI node 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_ui provides a [ContentSized] implementation that supports Text and UiImage 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 [UiDsl] entails.