Get Userlocation from map control

### Description

It would be nice to get the geo-userlocation, which is shown on the map if it is enebaled with IsShowingUser.

### Public API Changes

```csharp
Microsoft.Maui.Controls.Maps map;
map.IsShowingUser = true;
Location loc = map.GetCurrentUserLocation()
```

### Intended Use-Case

Get the current Position without own Location logic and code.