Disable assembly preload by default

Disable the current default behavior of Xamarin.Android runtime to
preload all the assemblies shipped in the apk on application startup.
This behavior has been the default in order to support older versions of
`Xamarin.Forms`, sacrificing startup performance.

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -290,7 +290,8 @@ Copyright (C) 2011-2012 Xamarin. All rights reserved.
 	<AndroidMakeBundleKeepTemporaryFiles Condition=" '$(AndroidMakeBundleKeepTemporaryFiles)' == '' ">False</AndroidMakeBundleKeepTemporaryFiles>
 
 	<!-- If true it will cause all the assemblies in the apk to be preloaded on startup time -->
-        <_AndroidEnablePreloadAssembliesDefault>True</_AndroidEnablePreloadAssembliesDefault>
+        <_AndroidEnablePreloadAssembliesDefault Condition=" '$(UsingAndroidNETSdk)' == 'true' ">False</_AndroidEnablePreloadAssembliesDefault>
+        <_AndroidEnablePreloadAssembliesDefault Condition=" '$(UsingAndroidNETSdk)' == 'false' ">True</_AndroidEnablePreloadAssembliesDefault>
 	<AndroidEnablePreloadAssemblies Condition=" '$(AndroidEnablePreloadAssemblies)' == '' ">$(_AndroidEnablePreloadAssembliesDefault)</AndroidEnablePreloadAssemblies>
 	<_NativeAssemblySourceDir>$(IntermediateOutputPath)android\</_NativeAssemblySourceDir>
 	<_AndroidUseNewTypemaps>True</_AndroidUseNewTypemaps>