Remove ConstructorExtensions.fs

[bamarsha]

The New methods defined in https://github.com/microsoft/qsharp-compiler/blob/main/src/QsCompiler/Core/ConstructorExtensions.fs can't be accessed from C#. This is problematic when changing the fields of a record, since the New methods can go through a deprecation period, but the default autogenerated record constructor can't (it always matches the current record fields).

Moving all of these methods to their original record modules would make them accessible from C#, and then this file can be removed.