T extends num> constructor
Create a mutable rectangle spanned by
(left, top) and
The rectangle contains the points
with x-coordinate between
left + width, and
with y-coordinate between
top + height, both inclusive.
height should be non-negative.
height are negative, they are clamped to zero.
height are zero, the "rectangle" comprises only the single
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;