The optional width to take into account.
The relative center X position, optionally offset by width.
auto bounds = TextBufferBounds(0, 0, 10, 0); assert(bounds.centerX == 5); assert(bounds.centerX(2) == 4); assert(bounds.centerX(5) == 2); bounds.left = 20000; assert(bounds.centerX == 5); // centerX provides a relative point, not absolute.
Finds the relative center point on the X axis, optionally taking into account the width of another object (e.g. text).