XmlSerializer.GenerateSerializer should not be in System.Private.Xml

[stephentoub]

System.Private.Xml contains all of the code for generating an assembly as the core logic behind the sgen tool:
https://github.com/dotnet/corefx/tree/master/src/Microsoft.XmlSerializer.Generator
The vast majority of the functionality here isn't used by anything other than sgen, which calls XmlSerializer.GenerateSerializer via reflection, and is the only caller of that method. This functionality should be removed from XmlSerializer in System.Private.Xml and moved into sgen.

[tamlin-mike]

I maintain code that uses System.Xml.Serialization.XmlSerializer.GenerateSerializer (directly, not using reflection) for a case sgen is unable to handle.

Could completely ripping this function out break f.ex. the Microsoft.XmlSerializer.Generator nuget package?

[StephenBonikowsky]

@mconnew Please comment on this issue and resolve as appropriate.