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/decode_test.go b/encoding/openapi/decode_test.go
index b3d417d..8a6d8a8 100644
--- a/encoding/openapi/decode_test.go
+++ b/encoding/openapi/decode_test.go
@@ -27,12 +27,12 @@
 	"github.com/stretchr/testify/assert"
 	"golang.org/x/tools/txtar"
 
+	"cuelang.org/go/cue"
 	"cuelang.org/go/cue/errors"
 	"cuelang.org/go/cue/format"
 	"cuelang.org/go/encoding/json"
 	"cuelang.org/go/encoding/openapi"
 	"cuelang.org/go/encoding/yaml"
-	"cuelang.org/go/internal/legacy/cue"
 )
 
 // TestDecode reads the testdata/*.txtar files, converts the contained