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/fs/ent/file.go

@@ -46,8 +46,7 @@ type FileEdges struct {
 func (e FileEdges) ParentOrErr() (*File, error) {
 	if e.loadedTypes[0] {
 		if e.Parent == nil {
-			// The edge parent was loaded in eager-loading,
-			// but was not found.
+			// Edge was loaded but was not found.
 			return nil, &NotFoundError{label: file.Label}
 		}
 		return e.Parent, nil

examples/fs/ent/file_query.go

@@ -22,13 +22,12 @@ import (
 // FileQuery is the builder for querying File entities.
 type FileQuery struct {
 	config
-	limit      *int
-	offset     *int
-	unique     *bool
-	order      []OrderFunc
-	fields     []string
-	predicates []predicate.File
-	// eager-loading edges.
+	limit        *int
+	offset       *int
+	unique       *bool
+	order        []OrderFunc
+	fields       []string
+	predicates   []predicate.File
 	withParent   *FileQuery
 	withChildren *FileQuery
 	// intermediate query (i.e. traversal path).