cmd/cue: embed support is no longer experimental

While the feature can still be disabled via CUE_EXPERIMENT,
it's on by default as of v0.12.0 after the proposal was accepted,
so it can be safely relied on as a stable feature.

Add a reminder for removing the ability to disable this experiment
on the v0.14 release. It's likely that the v0.13 release will follow
not long after v0.12, so we should give it a few more months
before we take away the option to disable the feature.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I2a46bcfd8c2bac14c9ad7372faf8828782e728d0
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1209274
Reviewed-by: Roger Peppe <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

cmd/cue/cmd/help.go

@@ -252,9 +252,9 @@ Files containing multiple documents cannot be embedded directly.
 For NDJSON or multi-document YAML files, embed as type=text
 and use APIs like yaml.Extract to decode as a list.
 
-Note that embedding cue files is not supported at this time.
+Note that embedding CUE files is not supported at this time.
 
-Note: support for embed is experimental, and can be disabled via
+For the time being, embedding support can still be disabled via
 CUE_EXPERIMENT=embed=0.
 
 For more details and discussion, see the proposal linked from

internal/cueexperiment/exp.go

@@ -16,6 +16,7 @@ var Flags struct {
 	EvalV3 bool
 
 	// Embed enables file embedding.
+	// TODO(v0.14): deprecate this flag to forbid disabling this feature.
 	Embed bool `envflag:"default:true"`
 
 	// DecodeInt64 changes [cuelang.org/go/cue.Value.Decode] to choose