Implement support for horizontally-shifted data updates

[t-mullen]

I am submitting a...

• Feature request

Issue description

When we update data, the point elements are animated vertically from their old data value to their new one. When the updated data is a horizontal translation of the previous (such as a sliding window of realtime data), this causes large and confusing changes in the graph during the animation.

We should add the option to specify the data is a translation and match point elements to their translated values.

For example, we have the data:

{
   labels: [0, 1, 2, 3, 4, 5],
   data: [200, 100, 800, 900, 100, 5]
}

We can update the data, specifying that it is a translation of the previous data.

chart.setData([100, 800, 900, 100, 99], { translation: -1 })

This will probably be difficult to implement given the current codebase, but it's necessary if we want to support real-time data.

[theiliad]

This is relevant to our continuous x-scale requirement. Would be great if we can add this functionality once those scale are added.