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.