Preferences API not working correctly on Windows

[tekmun]

Description

Preferences.Get returns 0 instead of null when key is never set before.
Preferences.Remove returns 0 instead of being deleted.
Picker ItemSource does not show a drop-down list. Nothing is shown.

Steps to Reproduce

Just create a Preferences.Get("test", "-1") and you will get 0 instead of null.
Just create a Preferences.Set("test", "1"). Then, Preferences.Remove("test"). Do a Preferences.Get("test", "-1") and you will get 0.
Do a picker. Populate it's ItemSource with a list. Nothing shows up when you click on it.

All these issues work well on Android platform.

Version with bug

6.0.486 (current)

Last version that worked well

6.0.400

Affected platforms

Windows

Affected platform versions

Windows SDK

Did you find any workaround?

NO.

Relevant log output

No log output.

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[mattleibow]

I had a dodgy feeling about this one so had a look. Seems this was a regression introduced in #8536. This was not caught as our tests coincidentally used the same default value as the type default. I am fixing and adding more tests to ensure this does not happen agian.

Specifically:

https://github.com/dotnet/maui/pull/8536/files#diff-6ed591e38dc7754551705bf5bb96f992115c384d19166e8dcda76267e177fb0cR36-R37