Publish Sentry.Android.AssemblyReader as a separate nuget package

[mattjohnsonpint]

This updates the AndroidAssemblyReader and related classes to be published in a separate nuget package. That allow us to consume it both from Sentry for .NET Android targets, and from Sentry.Xamarain, without affecting other targets. That will fix #2126, and allow us to get debug information in Xamarin apps, which will address getsentry/sentry-xamarin#134.

Also did some cleanup in here around global usings that came up while splitting it out, and improved the build process by replacing the update-test-apks.ps1 script with some MSBuild tasks.

[vaind]

I've just realized... any way to make this work for Unity as well, while changing things up?

[mattjohnsonpint]

I've just realized... any way to make this work for Unity as well, while changing things up?

I think it will just work. 🤞 We can try it in Unity after its published and make changes if Unity packages things differently.

[mattjohnsonpint]

I've just realized... any way to make this work for Unity as well, while changing things up?

I think it will just work. 🤞 We can try it in Unity after its published and make changes if Unity packages things differently.

@vaind - Looks like we would also need to adjust the path being searched in the APK, but shouldn't be too difficult I think.

getsentry/sentry-unity#1167