Add device specific unit testing

[ne0rrmatrix]

At the moment testing for device specific code is not implemented. In Media element there are many methods and classes that could be tested by using device specific testing. The Maui team has implemented this and we should figure out a way to test things or talk about a way forward with how we can test this going forward.

Another thing is we currently only test using Shell. There are other choices and testing for them would be a huge benefit for finding bugs in our code.

[phunkeler]

How does combining DeviceRunners with XHarness sound? I've found them quite effective and fairly easy to use both locally and in CI. However, their long-term prospects are somewhat uncertain.

[pictos]

do you have some sample or docs that we can take a look?

[phunkeler]

Nothing public at the moment but will try to put together a PoC in the coming days. Those repos + MAUI have some good examples.

[phunkeler]

I see #1444 is still open. Perhaps that's something we could expand on?