Enable `-s` as a convenience over `--self-contained`

[richlander]

This is a pretty common mode. Today, you can use -r to mean self-contained. We're changing that.

Proposal:

• Enable -s (or some other short-form like --sc) as a convenience over --self-contained.
• Use the SDK RID as an implicit RID if none is specified.

Proposed timeframe: 6.0.200.

Context: dotnet/designs#233 (comment)

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[marcpopMSFT]

I think the remaining issues are already tracked in 19725 and 21405 so closing this one.