[Enhancement] Add more descriptive exception for route not found (Shell.Current.GoToAsync).

[crwsolutions]

When no route is found, the following exception is thrown:

Relative routing to shell elements is currently not supported. Try prefixing your uri with ///: ///{originalRequest}

Because you are led astray by the hints in some situations I would suggest to rewrite it a bit and add another solution of global routing via Routing.RegisterRoute(). And when I am on it, I don't think that the first sentence is very helpful either. Because it's not entirely clear in some situations what it refers to. So I rather have something like 'Route not found.' So my suggestion would be to rewrite it to (I removed originalRequest because in my case that is very long and that could lead to TLDR;):

Route not found. Possible solutions could be prefixing your uri with '//' or '///' to use relative routing or register the route as global route for detail page routing.

This refers to:

maui/src/Controls/src/Core/Shell/ShellUriHandler.cs

Line 394 in 4e09b61

throw new Exception($"Relative routing to shell elements is currently not supported. Try prefixing your uri with ///: ///{originalRequest}");

Navigation docs: https://learn.microsoft.com/en-us/dotnet/maui/fundamentals/shell/navigation?view=net-maui-8.0