WebView NavigationEvent is NewPage for Back or Forward

### Description

WebNavigatingEventArgs.NavigationEvent is `NewPage` when navigating Back or Forward, instead of `Back` or `Forward`.

### Steps to Reproduce

Add breakpoint on the following line in MainPage.xaml.cs

```csharp
if (e.NavigationEvent == WebNavigationEvent.Back || e.NavigationEvent == WebNavigationEvent.Forward)
```
Start App.

Choose "Load Html" from Picker.

Right-click in WebView. Choose "Back". WebNavigatingEventArgs.NavigationEvent is `NewPage`.

Right-click in WebView. Choose "Forward". WebNavigatingEventArgs.NavigationEvent is `NewPage`.

### Link to public reproduction project repository

https://github.com/bobahop/MauiBugReport

### Version with bug

6.0.400

### Last version that worked well

Unknown/Other

### Affected platforms

Windows

### Affected platform versions

net6.0-windows10.0.19041.0

### Did you find any workaround?

_No response_

### Relevant log output

_No response_

Start with the public reproduction project and the breakpoint in MainPage.xaml.cs shown in the issue; run it on Windows and reproduce Back and Forward after choosing “Load Html.” Done means WebNavigatingEventArgs.NavigationEvent reports Back or Forward rather than NewPage for those actions.

Written by the indexing model from the issue text.