cue: make internal cue port main API implementation

- rm cue/*.go
- mv internal/legacy/cue/*.go cue/
- rename imports
- go

Change-Id: I553ce372ad457b1d73126b0a3f7be8224e415e80
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/6742
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/encoding/openapi/types.go b/encoding/openapi/types.go
index a216a08..ccc237a 100644
--- a/encoding/openapi/types.go
+++ b/encoding/openapi/types.go
@@ -20,10 +20,10 @@
 
 	"github.com/cockroachdb/apd/v2"
 
+	"cuelang.org/go/cue"
 	"cuelang.org/go/cue/ast"
 	"cuelang.org/go/cue/literal"
 	"cuelang.org/go/cue/token"
-	"cuelang.org/go/internal/legacy/cue"
 )
 
 // See https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.0.md#data-types