get an equivalent rectangle where the height and width are positive.

import { assertEquals } from "jsr:@std/assert"

const
my_rect: Rect = { x: -20, y: 100, width: 50, height: -30 },
my_abs_rect = positiveRect(my_rect)

assertEquals(my_abs_rect, {
x: -20,
y: 70,
width: 50,
height: 30,
})