Nothing preserves an assembly reference, if no C# types are used directly

### Android framework version

net8.0-android, net9.0-android

### Affected platform version

.NET 9

### Description

Context:

* https://github.com/xamarin/xamarin-android/pull/8954

In the above PR, I had to add a class named `Foo` and use it for the `CustomWidgetTests` to succeed.

The situation is:

* A class library with a custom view is used
* The custom view is only accessed from an `AndroidResource` .xml file
* The C# compiler drops the assembly reference, because no C# code references anything in the class library
* The assembly doesn't even get passed to the trimmer/linker

### Possible Solution

I suppose we could do something that would support passing *all* Android class libraries to the trimmer. Even ones that the C# compiler deems is unused?

We'd then rely on the trimmer to do its job to remove unused code.

### Steps to Reproduce

1. Remove `Foo.cs` from the changes in #8954
2. Run the APK tests in `Release` mode

### Did you find any workaround?

Reference some C# class, such as `Foo` or even the previous code would work:

```csharp
// usage of typeof(CustomTextView) includes the assembly reference
[DynamicDependency (DynamicallyAccessedMemberTypes.All, typeof (CustomTextView))]
```

### Relevant log output

Mentioned in 9a782d7f404d83240fb7dce9548fccbb0d679e17.

`Xamarin.Android.RuntimeTests.CustomWidgetTests` failed with:

```shell
(Binary XML file line #1 in Mono.Android.NET_Tests:layout/uppercase_custom: Binary XML file line #1 in Mono.Android.NET_Tests:layout/uppercase_custom: Error inflating class Mono.Android_Test.Library.CustomTextView)
at Java.Interop.JniEnvironment.InstanceMethods.CallObjectMethod(JniObjectReference , JniMethodInfo , JniArgumentValue* )
at Java.Interop.JniPeerMembers.JniInstanceMethods.InvokeVirtualObjectMethod(String , IJavaPeerable , JniArgumentValue* )
at Android.Views.LayoutInflater.Inflate(Int32 , ViewGroup )
at Xamarin.Android.RuntimeTests.CustomWidgetTests.<>c.b__0_0()
at NUnit.Framework.Constraints.VoidInvocationDescriptor.Invoke()
at NUnit.Framework.Constraints.ExceptionInterceptor.Intercept(Object )
--- End of managed Java.Lang.RuntimeException stack trace ---
android.view.InflateException: Binary XML file line #1 in Mono.Android.NET_Tests:layout/uppercase_custom: Binary XML file line #1 in Mono.Android.NET_Tests:layout/uppercase_custom: Error inflating class Mono.Android_Test.Library.CustomTextView
Caused by: android.view.InflateException: Binary XML file line #1 in Mono.Android.NET_Tests:layout/uppercase_custom: Error inflating class Mono.Android_Test.Library.CustomTextView
Caused by: java.lang.ClassNotFoundException: Mono.Android_Test.Library.CustomTextView
at java.lang.Class.classForName(Native Method)
at java.lang.Class.forName(Class.java:454)
at android.view.LayoutInflater.createView(LayoutInflater.java:815)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:1006)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:961)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:1123)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:1084)
at android.view.LayoutInflater.inflate(LayoutInflater.java:682)
at android.view.LayoutInflater.inflate(LayoutInflater.java:534)
at android.view.LayoutInflater.inflate(LayoutInflater.java:481)
at crc643df67da7b13bb6b1.TestInstrumentation_1.n_onStart(Native Method)
at crc643df67da7b13bb6b1.TestInstrumentation_1.onStart(TestInstrumentation_1.java:32)
at android.app.Instrumentation$InstrumentationThread.run(Instrumentation.java:2189)
Caused by: java.lang.ClassNotFoundException: Didn't find class "Mono.Android_Test.Library.CustomTextView" on path
```

In this case, `Mono.Android_Test.Library.CustomTextView` was used
from an Android layout, but not used anywhere in managed code.