UI per text section picking

[ickshonpe]

Objective

Allow picking text per section.

Fixes #17477

Solution

In ui_picking whenever a node with text components is below a pointer, don't add the Text node's entity to the hit_nodes list. Instead, iterate the list of text section bounding rects in its TextLayoutInfo component to find which text section the pointer is over, and add that section's entity id to the hit_nodes list.

• Add optional text components to NodeQuery.
• New helper function, pick_ui_text. Finds if a text section is hovered and returns its id.
• Add the entities of text sections to hit_nodes when hovered.
• Add the target camera entity to hit_nodes, instead of querying for it a second time.
• When a picked node is a text node and require_markers is enabled, check if the hit section entity has a Pickable component, instead of the text node.

This design might need to be changed later to allow for text selection and copying. But there doesn't seem any need to overcomplicate things for now by considering it.

Testing

I added observers to the TextBackgroundColors example's text entities. The observers turn a text section's text color to white when the pointer hovers them.

cargo run --example text_background_colors

[viridia]

Looks good.