This delays the resolution of the identifier in metadata, such the
parsed annotation expression is initially unresolved and
`Expression.resolve` must be called in order to resolve it.
This execises the support for references to identifiers declare via
macros, which will initially occur as unresolved identifiers.
Change-Id: I4863ce950ded0b9d2c1744421d9751cddea6e80c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/391641
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Jens Johansen <jensj@google.com>
Paul Berry