AndroidSdkInfo.AndroidNdkPath & ndk-bundle #92

Context: PR #90
Context: https://dev.azure.com/xamarin/public/_build/results?buildId=21603&view=logs&j=2d2b3007-3c5c-5840-9bb0-2b1ea49925f3

The "unrelated test failure" on Windows is because Windows is non-deterministic: the test asserts that given an Android SDK directory androidSdk which contains the file {androidSdk}\ndk-bundle\ndk-stack.cmd, then this:

var info = new AndroidSdkInfo (logger: null, androidSdkPath: androidSdk);

will return {androidSdk}\ndk-bundle as the info.AndroidNdkPath value.

The problem is that the info.AndroidNdkPath logic involves is doomed to fail. For starters, if the Registry has an NDK path configured, it is preferred:

https://github.com/xamarin/xamarin-android-tools/blob/3974fc38c0f25f943b5d3bf0a4e174532a2a60ee/src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkBase.cs#L61

If the Registry doesn't have a preferred NDK value, then we hit AndroidSdkWindows.GetAllAvailableAndroidNdks(), which involves a .Distinct() call:

https://github.com/xamarin/xamarin-android-tools/blob/3974fc38c0f25f943b5d3bf0a4e174532a2a60ee/src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkWindows.cs#L224-L268

which means that the order of returned directories is unknowable and may (will?) vary from test run to test run.

This is, in short, a highly "unstable" algorithm which won't be consistent from one run to the next. Which explains why it sometimes fails, and sometimes doesn't. :-(