spec: EBNF for struct types does not permit embedding instantiated types

[dominikh]

https://tip.golang.org/ref/spec#Struct_types defines

EmbeddedField = [ "*" ] TypeName .

with

TypeName  = identifier | QualifiedIdent .
QualifiedIdent = PackageName "." identifier .

if I am not mistaken, that doesn't permit the following valid program:

type S1[T any] struct{ F T }
type S2 struct{ S1[int] }

func main() { fmt.Println(S2{}.F) }

(https://go.dev/play/p/ZmKJ9hWyhOZ)

/cc @griesemer

Edit: LiteralType seems to have a similar issue for composite literals, via https://groups.google.com/g/golang-nuts/c/W_kqb9rfT5c

[cherrymui]

cc @griesemer @ianlancetaylor

[gopherbot]

Change https://go.dev/cl/411918 mentions this issue: spec: add missing optional type arguments after TypeName in syntax