[foldable] `SpanModeStateTrigger` not responding to span/unspan events

[conceptdev]

Description

Implementing a state trigger with TwoPaneView doesn't seem to work. Could be related to #5852 since it's probably an event not getting fired somewhere; might be fixed by same code too 🤞

Steps to Reproduce

1. Repros with the Sample App in the .NET MAUI source repo
2. Other Concepts -> Foldable -> shows a view with a TwoPaneView
3. Placing the XAML below on the Pane2 StackLayout

 <VisualStateManager.VisualStateGroups>
    <VisualStateGroup>
        <VisualState x:Name="Single">
            <VisualState.StateTriggers>
                <foldable:SpanModeStateTrigger SpanMode="SinglePane" />
            </VisualState.StateTriggers>
            <VisualState.Setters>
                <Setter Property="BackgroundColor" Value="DarkGreen" />
            </VisualState.Setters>
        </VisualState>
        <VisualState x:Name="DualLand">
            <VisualState.StateTriggers>
                <foldable:SpanModeStateTrigger SpanMode="Wide" />
            </VisualState.StateTriggers>
            <VisualState.Setters>
                <Setter Property="BackgroundColor" Value="Yellow" />
            </VisualState.Setters>
        </VisualState>
        <VisualState x:Name="DualPort">
            <VisualState.StateTriggers>
                <foldable:SpanModeStateTrigger SpanMode="Tall" />
            </VisualState.StateTriggers>
            <VisualState.Setters>
                <Setter Property="BackgroundColor" Value="Pink" />
            </VisualState.Setters>
        </VisualState>
    </VisualStateGroup>
</VisualStateManager.VisualStateGroups>

Link to public reproduction project repository

https://github.com/dotnet/maui

Version with bug

7.0 Release Candidate 2

Last version that worked well

Unknown/Other

Affected platforms

Android

Affected platform versions

Android 12L

Did you find any workaround?

No response

Relevant log output

No response

[ghost]

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.

[Zhanglirong-Winnie]

Verified this issue with Visual Studio Enterprise 17.9.0 Preview 1.1. Can repro this issue.