[net7.0] Use Environment.SpecialFolder.UserProfile, not SpecialFolder.Personal.

Context: dotnet/runtime#68610
Context: https://github.com/xamarin/xamarin-android-tools/commit/0be567a9

In Mono and .NET prior to .NET 8, the
[`System.Environment.SpecialFolder`][0]`.Personal` enum value would refer to
`$HOME` on Unix platforms.

This will be changing in .NET 8, such that
`Environment.SpecialFolder.Personal` will instead refer to
`$XDG_DOCUMENTS_DIR` (if set) or `$HOME/Documents`.  This is for "semantic
compatibility" with .NET on Windows.

Replace usage of `Environment.SpecialFolder.Personal` with
`Environment.SpecialFolder.UserProfile`, so that our code continues to work as
expected under .NET 8.

[0]: https://docs.microsoft.com/en-us/dotnet/api/system.environment.specialfolder?view=net-6.0

Backport of ##107.

Xamarin.MacDev/AppleSdkSettings.cs

@@ -142,7 +142,7 @@ namespace Xamarin.MacDev
 		
 		static AppleSdkSettings ()
 		{
-			var home = Environment.GetFolderPath (Environment.SpecialFolder.Personal);
+			var home = Environment.GetFolderPath (Environment.SpecialFolder.UserProfile);
 			var preferences = Path.Combine (home, "Library", "Preferences", "Xamarin");
 
 			if (!Directory.Exists (preferences))

Xamarin.MacDev/MobileProvision.cs

@@ -59,7 +59,7 @@ namespace Xamarin.MacDev
 			if (Environment.OSVersion.Platform == PlatformID.MacOSX
 				|| Environment.OSVersion.Platform == PlatformID.Unix)
 			{
-				string personal = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
+				string personal = Environment.GetFolderPath(Environment.SpecialFolder.UserPersonal);
 				ProfileDirectory = Path.Combine(personal, "Library", "MobileDevice", "Provisioning Profiles");
 			}
 			else

Xamarin.MacDev/MobileProvisionIndex.cs

@@ -1,4 +1,4 @@
-//
+//
 // MobileProvisionIndex.cs
 //
 // Author: Jeffrey Stedfast <jeff@xamarin.com>
@@ -199,7 +199,7 @@ namespace Xamarin.MacDev
 
             if (Environment.OSVersion.Platform == PlatformID.Unix || Environment.OSVersion.Platform == PlatformID.MacOSX)
             {
-                xamarinFolder = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Personal), "Library", "Xamarin");
+                xamarinFolder = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.UserProfile), "Library", "Xamarin");
             }
             else
             {