[release/6.0.4xx] fix support for $(AotAssemblies) property

[jonathanpeppers]

After 48f6b30 went in, building with $(AotAssemblies) can fail with a specific combination:

dotnet build -c Release -p:AotAssemblies=true -p:RunAOTCompilation=false
Microsoft.Android.Sdk.Aot.targets(26,33): error MSB4236:
The SDK 'Microsoft.NET.Runtime.MonoAOTCompiler.Task' specified could not be found.

This pack was renamed to:

Microsoft.NET.Runtime.MonoAOTCompiler.Task.net6

We only need to know the name of this pack due to supporting the old
$(AotAssemblies) property:

<ImportGroup Condition=" '$(MonoAOTCompilerTasksAssemblyPath)' == '' and '$(AotAssemblies)' == 'true' ">
  <Import Project="Sdk.props" Sdk="Microsoft.NET.Runtime.MonoAOTCompiler.Task.net6" />
  <Import Project="Sdk.props" Sdk="Microsoft.NETCore.App.Runtime.AOT.Cross.net6.android-x86" />
  <Import Project="Sdk.props" Sdk="Microsoft.NETCore.App.Runtime.AOT.Cross.net6.android-x64" />
  <Import Project="Sdk.props" Sdk="Microsoft.NETCore.App.Runtime.AOT.Cross.net6.android-arm" />
  <Import Project="Sdk.props" Sdk="Microsoft.NETCore.App.Runtime.AOT.Cross.net6.android-arm64" />
</ImportGroup>

$(RunAOTCompilation) is the new property that is handled by the Mono
workload.

For now we can change the names here, but should consider dropping the
$(AotAssemblies) property in a future release.

[jonpryor]

@jonathanpeppers wrote:

but should consider dropping the $(AotAssemblies) property in a future release.

As part of that process, we'll need to add/emit a warning mentioning this deprecation. Ideally we can have .NET 7 emit this warning, and in .NET 8 we can remove support for the $(AotAssemblies) property.

[jonathanpeppers]

I filed this for now: #7297

This PR is for .NET 6, but we should warn in 7 and remove/error in 8.

[jonathanpeppers]

I'm going to merge this to try to get the CI greener, failures seem OK:

• One test failed with:

System.Net.WebException : An error occurred while sending the request.
----> System.Net.Http.HttpRequestException : An error occurred while sending the request.
----> System.IO.IOException : Unable to read data from the transport connection: Connection reset by peer.
----> System.Net.Sockets.SocketException : Connection reset by peer

• Build_No_Changes MSBuild perf test - can ignore
• provisionator.exe failures, trying to address in [build] disable classic tests on .NET 6 release branches #7286