Serialization and deserialization of the typechecking data

[psfinaki]

Part of the Stage 2 as per the design doc.

[github-actions]

❗ Release notes required

@psfinaki,

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src/Compiler	docs/release-notes/.FSharp.Compiler.Service/9.0.200.md	No release notes found or release notes format is not correct

[psfinaki]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[psfinaki]

I'll be merging this. There are some very random test failures, don't really understand the pattern there, but cannot repro locally either... will look separately.

Otherwise, CheckedImplFile pickling/unpickling seems to more or less work, TcState is coming up!