Fix buggy interaction with widgets outside of clip rect

[emilk]

This fixes a bug which sometimes would make it possible to interact with widgets that were outside the parent clip_rect.

Interaction with a widget is done with the interact_rect, which is the intersection of the widget rect and the parent clip rect. If these rectangles are disjoint (the widget is outside the parent clip rect), this results in a negative rectangle (a rectangle with a negative width and/or height). The distance tests for negative rectangles were broken, causing the bug.

• This is part of solving https://github.com/emilk/egui/issues/4475
• It is also likely this would have solved https://github.com/emilk/egui/issues/4349 (which now has another fix for it)

Breaking changes

Rect::distance_to_pos, distance_sq_to_pos, signed_distance_to_pos now all return f32::INFINITY if the rectangle is negative.