[mono-2018-10] Include 'libmono-native.so' in .apk

[alexischr]

No description provided.

[alexischr]

This patch also contains this amendment suggested here: #2658 (comment).

Now libmono-native.so is definitely included in the apk (before it wasn't when I was building HelloWorld.csproj locally). However I am getting new test failures:

/Users/builder/jenkins/workspace/xamarin-android-pr-builder-debug/xamarin-android/bin/Debug/lib/xamarin.android/xbuild/Xamarin/Android/lib/armeabi-v7a/libmono-native.so : warning XA4301: Apk already contains the item lib/armeabi-v7a/libmono-native.so; ignoring. [/Users/builder/jenkins/workspace/xamarin-android-pr-builder-debug/xamarin-android/bin/TestDebug/temp/CheckSignApk(True,False)/UnnamedProject.csproj]

@jonp and others: Do you think that the BuildApk.cs change is superfluous after the Condition was "fixed"? If I were to keep one of the changes, which one should I try? (I have trouble testing this locally, and these builds take 6 hours). Or is the extra adding unrelated?

(Also: the FileSystemWatcher tests still fail, so the libmono-native entry points are still not being found)

[jonpryor]

I believe that this line is superfluous with BuildApk.cs line 415: Only one of the two lines should be needed, not both, as @(AndroidNativeLibrary) should cause an AddNativeLibrary() invocation to occur.