[msbuild] only include `@(ProguardConfiguration)` in apps

[jonathanpeppers]

Context: https://github.com/xamarin/AndroidX/pull/729 Context: https://github.com/xamarin/xamarin-android/pull/8025

A customer reported a build error such as:

C:\Program Files\dotnet\packs\Microsoft.Android.Sdk.Windows\33.0.46\targets\Microsoft.Android.Sdk.AndroidLibraries.targets(77,5):
error XACAAR7014: System.OutOfMemoryException: Exception of type 'System.OutOfMemoryException' was thrown.
at System.Text.StringBuilder.ToString()
at Xamarin.Android.Tasks.CreateAar.RunTask()
at Microsoft.Android.Build.Tasks.AndroidTask.Execute()

Somewhere here:

https://github.com/xamarin/xamarin-android/blob/c31f3eda63a16e412a39fa61eb0f885be3c5f543/src/Xamarin.Android.Build.Tasks/Tasks/CreateAar.cs#L108-L114

We have a compounding issue:

• Google Play Services NuGets add proguard.txt files to class libraries

• These make it to YourClassLibrary.aar

• You might have class libraries that reference other class libraries

• You end up with N^2 proguard.txt files and hit OOM.

Step 1 to fix this is to simply not add @(ProguardConfiguration) from the Google Play Services NuGets for class libraries.

We can solve the obj\Debug\lp\173\jl\proguard.txt entries in xamarin/xamarin-android#8025.

[jonathanpeppers]

/azp run

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[jonathanpeppers]

I guess I should not have done this from a fork. Is it fine to merge and we'll just react if something breaks?

Or I can close/reopen a new one.