entc/gen: add support for WithNamed<E> feature-flag (#2792)

* entc/gen: struct fields and methods for NamedEdge api

* entc/gen: generate WithNamedEdge methods for named-edges

* entc/gen: implement eager-loading for named-edges

* entc/gen: simplify eager-loading template

* entc/gen: drop support for unqiue edges in named-based loading

* all: codegen

* doc/website: named-edges feature-flag

* Update doc/md/eager-load.mdx

* Update doc/md/eager-load.mdx

examples/m2m2types/ent/group_query.go

@@ -29,8 +29,7 @@ type GroupQuery struct {
 	order      []OrderFunc
 	fields     []string
 	predicates []predicate.Group
-	// eager-loading edges.
-	withUsers *UserQuery
+	withUsers  *UserQuery
 	// intermediate query (i.e. traversal path).
 	sql  *sql.Selector
 	path func(context.Context) (*sql.Selector, error)

examples/m2m2types/ent/user_query.go

@@ -29,7 +29,6 @@ type UserQuery struct {
 	order      []OrderFunc
 	fields     []string
 	predicates []predicate.User
-	// eager-loading edges.
 	withGroups *GroupQuery
 	// intermediate query (i.e. traversal path).
 	sql  *sql.Selector