Allow for Plot Bounds Setting with Linked Axes

It seems as though there is no way to control the visible bounding box for plots that have been linked with a `LinkedAxisGroup`.

I have two plots that I have grouped with a `LinkedAxisGroup`. It seems as though there is no way for me to control the visible area through a bounding box and the autoscaling is not working because I have the linked axes.

**Describe the solution you'd like**
I looked in the source code and noticed that the `LinkedAxisGroup` has a `get` and `set` methods for the PlotBounds, but they are not public. Would it be possible to make those public?