Context

LogMessagePacketBase provides a type-safe way to wrap BuildEventArgs into a node packet for IPC serialization.

For the RAR node to replay log events, it makes sense to reuse existing serialization wrappers instead of introducing another shim & reimplementing serialization for each event type.

However, right now LogMesssagePacketBase has a bit of a complex dependency chain - depending on preprocessor directives, certain events will either use a cached delegate of the base serialize methods, add additional properties to be serialized, or fully ignore the base implementation and provide a custom serializer. Another point is that many types in this path only exist in Microsoft.Build.dll (ArrayDictionary, ItemDictionary, PropertyDictionary, ect.).

One key here is that this additional logic is only relevant for Microsoft.Build.dll. Since MSBuild.dll, MSBuildTaskHost.dll, and (next) Microsoft.Build.Tasks.dll all use the default serialization, this custom logic can be refactored out, which removes the need for any conditional compilation.

Changes made

• Remove compile directives from LogMessagePacketBase.
• Move custom logic for Microsoft.Build.dll into its LogMessagePacket implementation.
• Add virtual EventCanSerializeItself to mimic compile directive logic.
• Virtualize WriteEventToStream and ReadEventFromStream to allow hooking in custom serializers.
• Replace TargetFinishedTranslator delegate with virtual TranslateAdditionalProperties to allow serializing additional properties to the defaults.
• De-abstract LogMessagePacketBase, as other assemblies only need the default implementation.

Note that this doesn't touch any of the actual serialization logic or build event types, just the packet wrapper - so this shouldn't require a version rev or introduce compatibility breaks.