evalv3 closedness regression with embeddings and definitions

[mvdan]

# With the old evaluator.
env CUE_EXPERIMENT=evalv3=0
exec cue export

# With the new evaluator.
env CUE_EXPERIMENT=evalv3=1
env CUE_DEBUG=openinline=0
exec cue export

-- input.cue --
package p

_globals: glb: globalField: ""

#GlobalContext: globalField: string
#Context: {
	glb: #GlobalContext
	out: glb
}
out: {
	ingress: {
		#Ingress & {
			#def: (#Context & _globals).out
		}
	}

	ingress?: {
		foo: 1234
		bar: "http"
	}
}
#Embed: #def: {}

#Ingress: {
	#Embed
	...
}

as of 72567b9:

# With the old evaluator. (0.011s)
> env CUE_EXPERIMENT=evalv3=0
> exec cue export
[stdout]
{
    "out": {
        "ingress": {
            "foo": 1234,
            "bar": "http"
        }
    }
}
# With the new evaluator. (0.023s)
> env CUE_EXPERIMENT=evalv3=1
> env CUE_DEBUG=openinline=0
> exec cue export
[stderr]
out.ingress.bar: field not allowed:
    ./input.cue:19:3
out.ingress.foo: field not allowed:
    ./input.cue:18:3
[exit status 1]

Once again reduced from @alecholmez's project in Unity.

[mpvl]

Reduced to this:

x: { A & __no_sharing }
x: y: 1
#B: {}
A: {
	#B
	...
}