[ember-data] Model#eachRelationship fixes (#27278)

types/ember-data/index.d.ts

@@ -526,7 +526,7 @@ declare module 'ember-data' {
              * invoking the callback with the name of each relationship and its relationship
              * descriptor.
              */
-            eachRelationship(callback: Function, binding: any): any;
+            eachRelationship(callback: (name: string, details: RelationshipMeta<this>) => void, binding?: any): any;
             /**
              * Represents the model's class name as a string. This can be used to look up the model's class name through
              * `DS.Store`'s modelFor method.
@@ -577,7 +577,7 @@ declare module 'ember-data' {
              * invoking the callback with the name of each relationship and its relationship
              * descriptor.
              */
-            static eachRelationship(callback: Function, binding: any): any;
+            static eachRelationship<M extends Model = Model>(callback: (name: string, details: RelationshipMeta<M>) => void, binding?: any): any;
             /**
              * Given a callback, iterates over each of the types related to a model,
              * invoking the callback with the related type's class. Each type will be

types/ember-data/test/relationships.ts

@@ -12,6 +12,20 @@ const Polymorphic = DS.Model.extend({
     paymentMethods: DS.hasMany('payment-method', { polymorphic: true })
 });
 
+Polymorphic.eachRelationship(() => '');
+Polymorphic.eachRelationship(() => '', {});
+Polymorphic.eachRelationship((n, meta) => {
+    let s: string = n;
+    let m: 'belongsTo' | 'hasMany' = meta.kind;
+});
+let p = Polymorphic.create();
+p.eachRelationship(() => '');
+p.eachRelationship(() => '', {});
+p.eachRelationship((n, meta) => {
+    let s: string = n;
+    let m: 'belongsTo' | 'hasMany' = meta.kind;
+});
+
 class Comment extends DS.Model {
     author = DS.attr('string');
 }