#### Background
While cyclic assembly references are unusual they are supported by the runtime and encountered in practice. In our project we use a version of Xamarin.Forms retargeted for a modern .NET (as a stopgap solution before an update to full MAUI stack). Xamarin.Forms historically come with such an assembly cycle: `Xamarin.Forms.Core.dll` -> `Xamarin.Forms.Platform.dll` -> `Xamarin.Forms.Platform.iOS.dll` -> `Xamarin.Forms.Core.dll`. This is produced by first compiling `Xamarin.Forms.Core.dll` against a dummy `Xamarin.Forms.Platform.dll` (`netstandard2.0` assembly). Then the Platform assemblies are built, and finally forwarder versions of `Xamarin.Forms.Platform.dll` are created for each platform. This is all packaged into NuGets in such a way that each TFM gets the same `Xamarin.Forms.Core.dll` but a different set of `Xamarin.Forms.Platform.dll` and `Xamarin.Forms.Platform.<platform>.dll` assemblies.
#### Problem
With current workloads each incremental rebuild fails with:
```
/usr/local/share/dotnet/packs/Microsoft.iOS.Sdk/16.4.7125/targets/Xamarin.Shared.Sdk.targets(1047,3): error : Encountered an assembly reference cycle related to the assembly obj/Debug/net7.0-ios/iossimulator-arm64/linked/Xamarin.Forms.Core.dll
```
#### Solution
The PR updates the algorithm in `AOTCompile` to detect cycles using [Tarjan's algorithm](https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm) for finding [strongly connected components](https://en.wikipedia.org/wiki/Strongly_connected_component) in a graph. When a cycle is detect any assembly in the cycle is considered up-to-date only if all the assemblies in the cycle are up-to-date.
With this change the project does incremental rebuilds correctly. I verified in the build output that the assembly cycle is considered up-to-date, and that any changes to the application assemblies still return `false` from the up-to-date check and get rebuilt.
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Co-authored-by: Filip Navara <filip.navara@gmail.com>
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