style tag not propagating to sub-ki.Props map -- need to pass down from owner

[rcoreilly]

editing a ki.Props map will offer type options for the instance{} type based on the ki.PropTag() method, but if you have a sub-ki.Props map, it won't have a ki owner to get it from. So we need to propagate the PropTag down. Probably best to just store it separately on ValueViewBase and anyone who has a ki owner overwrites but otherwise inherit.

[rcoreilly]

editing props is not a common use-case in actual apps.. lowpri.