Bring back exception serialization support

[ViktorHofer]

We see strong customer demand for being able to serialize Exceptions with BinaryFormatter or DCS.

The following actions are required:

• Make coreclr exception types serializable, add typeforwards and bring back serialization implementation (Make coreclr exceptions serializable and add typeforwards coreclr#14311)
• Mirror in corert
• Make corefx exception types serializable, add typeforwards and bring back serialization implementation (Make corefx exceptions serializable and add typeforwards corefx#24427)
• Add typeforwards for internal types (Make corefx exceptions serializable and add typeforwards corefx#24427)
• Add tests in System.Runtime.Serialization.Formatters.Tests
• Port to release branches
• Update docs

cc @jkotas @stephentoub @danmosemsft

[4creators]

With which version will this change be shipped?

[danmoseley]

@4creators definitely in 2.1. We are exploring the possibility of servicing 2.0 for it. Generally we don't service for "features" but this is necessary for some customers to port successfully. Do you need it?

[4creators]

Yeah, unfortunately I need it for all custom exceptions I use in every library I work on 😒

[danmoseley]

@4creators custom exceptions in general should be serializable already, as in 2.0 we made Exception do all necessary work to serialize. They just need to call the base. The problem is other exceptions we ship.

[4creators]

@danmosemsft My implementation pattern for throwing exceptions is to derive from every framework exception I want to throw my own exception i.e. CustomInvalidOperationException etc. Therefore Exception is not enough and I can not derive from Exception either as this would be braking change for error handling code where I do it seperatly for my CustomInvalidOperationException and framework InvalidOperationException. And I have a lot's of them and a lot of error handling paths.

[danmoseley]

Got it.