[One .NET] $(AndroidEnablePreloadAssemblies)=False by default (#5790) (…

…#5914)

Fixes: #5838
Context: e0da1f1

Partially reverts 522d7fb which, reverted d13d0f9.

The [`$(AndroidEnablePreloadAssemblies)`][0] property controls whether
or not *all* `.dll` files contained within a `.apk` are loaded during
process startup.  *Not* doing so reduces process startup times, which
is desirable, but this also caused certain Xamarin.Forms apps to fail
to run as they previously had, as not loading all assemblies during
startup broke their Dependency Injection infrastructure.

For .NET 6, we feel we have *some* "wiggle-room" to change default
semantics, so for .NET 6 projects set the default value of
`$(AndroidEnablePreloadAssemblies)` to False, so that assemblies are
*not* pre-loaded during process startup.

`$(AndroidEnablePreloadAssemblies)` can be set to True within the
app's `.csproj` file to return to "legacy" semantics.  This will cause
all assemblies to be loaded during startup, with a commensurate
increase in app startup overheads.

[0]: https://docs.microsoft.com/en-us/xamarin/android/deploy-test/building-apps/build-properties#androidenablepreloadassemblies

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest.cs

@@ -3938,7 +3938,11 @@ public void PackageNamingPolicy ([Values ("LowercaseMD5", "LowercaseCrc64")] str
 				Assert.IsTrue (b.Build (proj), "build should have succeeded.");
 				var environment = b.Output.GetIntermediaryPath (Path.Combine ("__environment__.txt"));
 				FileAssert.Exists (environment);
-				Assert.AreEqual ($"__XA_PACKAGE_NAMING_POLICY__={packageNamingPolicy}", File.ReadAllText (environment).Trim ());
+				if (Builder.UseDotNet) {
+					Assert.AreEqual ($"__XA_PACKAGE_NAMING_POLICY__={packageNamingPolicy}{Environment.NewLine}mono.enable_assembly_preload=0", File.ReadAllText (environment).Trim ());
+				} else {
+					Assert.AreEqual ($"__XA_PACKAGE_NAMING_POLICY__={packageNamingPolicy}", File.ReadAllText (environment).Trim ());
+				}
 			}
 		}
 

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

@@ -291,7 +291,8 @@ 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)' != 'true' ">True</_AndroidEnablePreloadAssembliesDefault>
 	<AndroidEnablePreloadAssemblies Condition=" '$(AndroidEnablePreloadAssemblies)' == '' ">$(_AndroidEnablePreloadAssembliesDefault)</AndroidEnablePreloadAssemblies>
 	<_NativeAssemblySourceDir>$(IntermediateOutputPath)android\</_NativeAssemblySourceDir>
 	<_AndroidUseNewTypemaps>True</_AndroidUseNewTypemaps>