mark-shipped.ps1 doesn't produce stable results across OSes

[RikkiGibson]

Our public APIs in release/dev16.7 were marked shipped via scripts/PublicApi/mark-shipped.ps1 on a Linux machine. If we run the script again on Windows it produces this diff:
release/dev16.7...RikkiGibson:shuffle

(running the script on Mac on release/dev16.7 branch produces no diff in the relevant paths.)

It also appears that the tool seems to reorder existing method overloads in undesirable ways across releases: for example, changing default parameter values on method overloads can cause the overloads to appear in a different order. #48059 (comment)

Reordering members when running marked-shipped.ps1 harms the reviewability of public API changes. Obviously there are likely problems around "when I change this about an overload, do we consider it the same method as before?" but it feels like at least things which do not change the signature of a method from the runtime point of view should not affect sort order.

[Youssef1313]

A little bit related to dotnet/runtime#20109 (comment)