fix(localizePoint): modify point in-place (match browser behavior)

Browser behavior is to update and return the point passed in.  Update
ios to do the same.  Though this is a breaking change, the change
shouldn't be too noticable since this function is internal to devkit
and used primarily by input handling.  In timestep, JavaScript
explicitly creates new points when necessary and otherwise assumes
localizePoint will not return a new point.  As a result, calls such as
`localizePoint(new Point(pt))` previously returned Point objects in
the browser, but raw objects on ios.  Any code relying on input event
points being instances of a Point (having Point methods) failed on
iOS.

While it makes iOS input dispatch slightly faster, it is unknown
whether this will actually be a meaningful increase.

Breaks any code relying on different ios and browser behavior of input
event points.  iOS input event points are now instances of Point
rather than simple {x, y} objects.