feat: implement Rect ops for moving
Implemented `Add`, `AddAssign`, `Sub`, and `SubAssign` on `Rect` for
`Offset`. This makes it possible to move rects
```rust
let rect = Rect::new(1, 2, 3, 4);
let moved = rect + Offset(1, 2);
let moved = rect - Offset(1, 2);
let moved = rect + Offset(-1, -2);
```
Additionally Rect, Size, Offset, and Position now all have MIN and MAX
consts.
96d097ef76