CUE encoding

[roman-mazur]

I found a case recently where I'd like to define a command that writes or prints CUE code. Would it make sense to introduce encoding/cue package with a function Marshal just like in encoding/json or encoding/yaml.

To illustrate

import (
  "encoding/cue"

  "tool/cli"
)

output: foo: "bar"

command: print: cli.Print & { text: cue.Marshal(output) }

I understand that I can solve some of the cases with cue eval -e output, but it still seems more limited compared to having the CUE encoding.

[myitcv]

Please see #1852