WPF / WinUI3 control / ConPTY example (included)

I am aware the ConPTY / wpf control are not yet meant for wide/production use (#6999) . I figured I would put a better example for them working together in a way other users might use it.

From some limited testing it actually works very well.

https://github.com/mitchcapper/ConPtyTermEmulator

Happy to contribute the example here but wasn't quite sure if best to do a PR and if so to where in the repo. There is an airspace issue I don't know if resolvable (some controls allow you to add children to the control itself so those appear on top of the native window.

I think the nuget package may also need restructuring as The ConPTY OpenTerminal.exe did not end up where the native code expected it.

It would be nice if there was a way to get the terminal buffer as well. If there was a select all it would be somewhat hackable with TerminalGetSelection but it doesn't look like it would be too hard to do a PR that is similar to GetSelectedText but for the whole buffer. Let me know if desired.

Start by reviewing the linked ConPtyTermEmulator example and the existing ConPTY/WPF control discussion in issue #6999. The issue names no repository files or tests, so the desired scope and completion criteria would need to be clarified before implementation.

Written by the indexing model from the issue text.