Implement FunctionExport serialization and fix a crash in AncestryInfo

[CrystalFerrai]

• FunctionExport had TODOs in its serialization code that should be completed by these changes. For reference, I looked at UFunction::Serialize in Class.cpp. The code is the same in UE 4.27 and UE 5.6. I have only tested with UE 5.6 assets.
• While creating test assets using UE 5.6, I managed to create one that triggered a crash in AncestryInfo.SetAsParent where the parameter dad had its Value property set to null which triggered a NullReferenceException when accessing dad.Value.Value.

Existing unit tests all passed.

[CrystalFerrai]

Here is the asset that triggered the crash in AncestryInfo.SetAsParent. I loaded the raw bytes (uasset and uexp) into an array and used code like this to read it.

UAsset asset = new(version);

using (MemoryStream stream = new(rawData))
using (AssetBinaryReader reader = new(stream, asset))
{
	asset.Read(reader);
}

TestActor.zip
(Engine version used to create the asset is 5.6.1)

[trumank]

I'm struggling to reproduce the crash here. I've tried adding as a regular test via:

TestUE5_6Subsection("TestActor", EngineVersion.VER_UE5_6);

and also loading the uasset + uexp manually and reading from a memory stream, but neither raise an exception on this line. The test only fails due to binary equality and unparsed exports.

Can you add a test demonstrating the crash and the fix?