Investigate independent input source for Swap Chain Panel

While reading some background documentation on how this whole co* stuff worked, I noticed that SwapChainPanel apparently has a provision to let background threads potentially mess with the chain instead of having to jump to the UI thread to do so:

https://docs.microsoft.com/en-us/uwp/api/windows.ui.xaml.controls.swapchainpanel.createcoreindependentinputsource#Windows_UI_Xaml_Controls_SwapChainPanel_CreateCoreIndependentInputSource_Windows_UI_Core_CoreInputDeviceTypes_

It's probably not easily/instantly applicable here. But I want to leave the note because I thought of it and @DHowett-MSFT and @zadjii-msft might have an opinion on whether that would be a decent follow-on task to generate from this comment.

Originally posted by @miniksa in https://github.com/microsoft/terminal/pull/4051/threads/MDIzOlB1bGxSZXF1ZXN0UmV2aWV3VGhyZWFkMjIzNTY3ODg3OnYy/unresolve

This represents investigating whether using this is a good idea or not.