Feature Request - Migrade HwndHost code into main repository

[amaitland]

Based on discussion in #4964 (comment)

This will move the HwndHost source out of it's own repository and into a HwndHost sub folder in the Wpf project.

This has a number of advantages, the HwndHost implementation is often left behind currently when something new is added/changed, so we can keep that in sync with minimal effort now.

Changing to how the package is published will be the thing.

[amaitland]

An example will be added to the MinimalExample.

cefsharp/CefSharp.MinimalExample#148

For now it will be just a modified version of the Wpf example