Migrate dagger.#Secret and dagger.#Stream to new format

- Refactored to keep every transformation of built-in types (e.g. FS,
  Secret, etc) to/from CUE in the same place (plancontext)
- dagger.#Service and dagger.#Secret are now following the new FS-like format
  (e.g. `_service: id: string`)
- Backward compatibility
- dagger.#Stream is now an alias for dagger.#Service

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

compiler/compiler.go

@@ -24,10 +24,6 @@ func NewValue() *Value {
 	return DefaultCompiler.NewValue()
 }
 
-func NewValueWithContent(x interface{}, selectors ...cue.Selector) (*Value, error) {
-	return DefaultCompiler.NewValueWithContent(x, selectors...)
-}
-
 // FIXME can be refactored away now?
 func Wrap(v cue.Value) *Value {
 	return DefaultCompiler.Wrap(v)
@@ -84,14 +80,6 @@ func (c *Compiler) NewValue() *Value {
 	return empty
 }
 
-func (c *Compiler) NewValueWithContent(x interface{}, selectors ...cue.Selector) (*Value, error) {
-	v := c.NewValue()
-	if err := v.FillPath(cue.MakePath(selectors...), x); err != nil {
-		return nil, err
-	}
-	return v, nil
-}
-
 func (c *Compiler) Compile(name string, src string) (*Value, error) {
 	c.lock()
 	defer c.unlock()