Create a mutable rectangle spanned by (left, top) and
(left+width, top+height).
The rectangle contains the points
with x-coordinate between left and left + width, and
with y-coordinate between top and top + height, both inclusive.
The width and height should be non-negative.
If width or height are negative, they are clamped to zero.
If width and height are zero, the "rectangle" comprises only the single
point (left, top).
Source
MutableRectangle(this.left, this.top, T width, T height)
: this._width = (width < 0) ? _clampToZero<T>(width) : width,
this._height = (height < 0) ? _clampToZero<T>(height) : height;