Replace MauiTestUtils with DeviceRunners nuget package

[jamescrosswell]

The device tests use a device runner Test App, which is a very simple MAUI application containing project references to all of our test projects. XHarness can be used to install and launch the test app on iOS and Android physical devices or simulators, run any xUnit tests referenced and then capture both test results and application logs as artefacts.

The mechanism used to discover and run xUnit tests within the test app is called Device Runners. Originally Microsoft made the Device Runners available as some sample code in thedotnet/maui repository, which we vendored into (i.e. copied into) the test/MauiTestUtils folder of the sentry/sentry-dotnet repo.

Since then, that code appears to have been turned into a semi-official Device Runners NuGet package, which is being actively maintained.

This PR removes our vendored in code - using a package reference to the most recent version of the NuGet package instead.

Hopefully this will make it easier for us to upgrade the device tests to net8.0 in a separate PR.

Notes to Reviewers

It looks like a lot to review but mostly it's deleting code:

• If you collapse the tests/MauiTestUtils directory, all of which is being deleted, it starts to look less overwhelming
• The test/Sentry.Maui.Device.TestApp/Platforms/Android/SentryInstrumentation.cs class is worth calling out... it's a custom instrumentation class that enables us to intercept launching of the device tests on Android (so we can inject environment variables that have been set on CI - mainly so we can skip certain flaky tests in CI)
• Most of the other changes are addressing flaky tests

Notes on Flaky Tests

There are a few tests that I had to disable on iOS and some others I had to disable on Android. On Android, it was only when targeting API 31 or 33 (the only two I tried other than 27). When this happens, the error message from Xharness is a bit misleading - it indicates the tests are timing out after 900 seconds.

This may be related to Restrictions on non-SDK interfaces but, if so, I don't understand how.

You can download a CSV describing ~656k API interfaces and the availability of each... so it's possible some of the APIs we're using in our device tests are not supported on API 33. How to know whether we're using any of the blocked/obsolete APIs though??? Maybe that information is in the adb logs if you know how to look for it but our adb logs are about 33k lines so that's a bit like trying to finding a needle in a haystack.

If we could work out what was going on there, we might be able to re-enable the Android tests. I don't have any leads for the iOS tests.

#skip-changelog

[bruno-garcia]

a bit concerned with the Skip calls. otherwise LGTM

[bruno-garcia]

Feel free to merge once u're comfortable with maintaining this, from my PoV looks good