Add a methods to compute the bounding rect of quadratic and cubic bezier curves

[nical]

We first need to reexport euclid's rectangle type (euclid::Rect<T>) in bezier/src/lib.rs the same way we reexport the Point type, and add a method:

fn bounding_rect(&self) -> Rect

To QuadraticBezierSegment and CubicBezierSegment.

[nical]

cc @o0Ignition0o

[nical]

After a discussion with @o0Ignition0o, I like his suggestion to compute the minimum bounding rect, so I suggest having two methods:

fn bounding_rect(&self) -> Rect

which is a naive implementation that returns the minimum rectangle containing the control points of the curve, and

fn minimum_bounding_rect(&self) -> Rect

Which is slightly more expensive but returns a tighter rect. find_y_inflection should be useful for this, and for some reason find_x_inflection is missing but it could be added. find_y_maximum is also relevant, but find_x_maximum, find_x_minimum and find_y_minimum are missing too (should not be hard to add the missing methods taking inspiration from the existing ones).

[o0Ignition0o]

This looks good, I'll give it a try ! I'm also considering rotating the curve to "flatten" the start and end points, before invoking find_y_maximum. I don't know if it would be the fastest implementation to get the minimum_bounding_rect, but I'll make a pr and see if I can improve it :)