cmd/cue: rethink vet

[myitcv]

cue vet is incredibly versatile as a tool to validate CUE and data. Possibly too versatile to the point that it doesn't serve specific use cases well enough. And yet it doesn't cover all possible use cases that one might imagine for such a command.

This is an umbrella issue to capture ideas for what cue vet v2 might look like.

The vet label is used to mark all cue vet-related issues for easy discovery: vet candidate for a vet rule to detect suspect usage

The list that follows is in no particular order and by no means complete. It is in effect an attempt to distill thoughts from the issues seen over time

• The tri-state of -c is confusing. We need to move away from this. cmd/cue: vet's -c flag may not be working as documented #2120 (comment)
• Have a -e-esque way of only vetting part of a configuration: cmd/cue: vet should also support a -e flag  #2400
• ...