[r8] update proguard rule to keep .NET runtime classes (#9044)

Context: dotnet/runtime#103016
Context: dotnet/runtime#103337

In dotnet/runtime we are adding a few more Java classes to assist with
.NET crypto. One was added in dotnet/runtime#103016, and another may
be added in dotnet/runtime#103337.

This PR changes ProGuard to keep all of the classes in this package
rather than individually adding them.

Co-authored-by: Alexander Köplinger <alex.koeplinger@outlook.com>

src/Xamarin.Android.Build.Tasks/Resources/proguard_xamarin.cfg

@@ -25,8 +25,8 @@
 -keep class md52ce486a14f4bcd95899665e9d932190b.** { *; <init>(...); }
 -keepclassmembers class md52ce486a14f4bcd95899665e9d932190b.** { *; <init>(...); }
 
-# .NET 8 runtime
--keep class net.dot.android.crypto.DotnetProxyTrustManager { *; <init>(...); }
+# .NET runtime
+-keep class net.dot.android.crypto.** { *; <init>(...); }
 
 # Android's template misses fluent setters...
 -keepclassmembers class * extends android.view.View {