[vx-bounds] add package with 'withBoundingRects()' HOC and tests

[williaster]

This PR adds the @vx/bounds package which contains a withBoundingRects() higher-order component that is meant to help with detecting whether a given component is overflowing its parent container. This HOC passes the following props to the component which it wraps:

const rectShape = PropTypes.shape({
  top: PropTypes.number.isRequired,
  right: PropTypes.number.isRequired,
  bottom: PropTypes.number.isRequired,
  left: PropTypes.number.isRequired,
  width: PropTypes.number.isRequired,
  height: PropTypes.number.isRequired,
});

export const withBoundingRectsProps = {
  getRects: PropTypes.func,
  rect: rectShape,
  parentRect: rectShape,
};

Tests
Tested with jest and with @vx/tooltip in a separate repository:

Naive tooltip (beforewithBoundingRects())

Smarter tooltip (after withBoundingRects())

[hshoff]

👏 fantastic work @williaster!