Support swipe actions from a given start point to an end point

With the currently existing API it's not possible to swipe in any arbitrary direction, but only in a defined `GREYDirection` (left, right, up or down).
Swiping in any direction, for example from a given start point to a given end point, might also be needed to test some UI components.

I propose adding new public swipe actions, that take a start point and an end point and perform a swipe along these points.

The API for the actions might look like this:

`grey_swipeFastFromStartToEndPoint(CGPoint startPoint, CGPoint endPoint);`
`grey_swipeSlowFromStartToEndPoint(CGPoint startPoint, CGPoint endPoint);`

---

The implementation might be either a new `GREYBaseAction` subclass, or by extending `GREYSwipeAction` with this functionality.

This can be implemented similar to the existing `GREYSwipeAction`, by using

`[GREYPathGestureUtils touchPathForDragGestureWithStartPoint: endPoint: cancelInertia:]`

instead of
https://github.com/google/EarlGrey/blob/d1f48ddee051172ecea83835f2495d9e1a501d8c/EarlGrey/Action/GREYSwipeAction.m#L127-L130

Start with EarlGrey/Action/GREYSwipeAction.m, especially the existing swipe implementation referenced in the issue, and compare it with GREYPathGestureUtils touchPathForDragGestureWithStartPoint:endPoint:cancelInertia:. Review how the current public swipe actions are exposed. Done means arbitrary start-to-end swipes are supported through the proposed fast and slow actions, with behavior consistent with existing swipe actions.

Written by the indexing model from the issue text.