Support auto skeleton item size calculation.

[puppywang]

In our real app usage, we would like not to supply the skeleton item size in RecyclerView.applySkeleton, we want it automatically calculated, so I create this simple PR, please check, thanks.

[Faltenreich]

Hi @puppywang, thank you for your contribution!

This improvement makes absolute sense and I will gladly add it to the library. Sadly your pull request does not work as expected yet. The demo app shows only one item at a time in its Skeleton as opposed to the three items that would have place. Maybe you can test this by yourself and improve your pull request.

Precondition: Set the skeletonItemSize of the RecyclerViewFragment to 0 in order to autocalculate the item count with your logic.

Thanks in advance and have a nice day!

[puppywang]

Got, I will try to fix it ASAP.