Add defaultName to all templates; validate in VS 16.8 Preview 2

[bartelink]

Per this writeup, VS will start supporting showing the templates in 16.8 Preview 2...

• The checklist mentions adding a defaultName as a best practice
• Also need to check stuff looks ok in VS

(Things work fine from the command line and Rider, so I'm tempted to close this soon on the assumption that it will Just Work)