refactor(forms): Add a lightweight DI token for Control (angular#64188)

This will allow optionally injecting the Control directive without
importing the full directive.

PR Close angular#64188

Author: mmalerba

goldens/public-api/forms/signals/index.api.md

@@ -10,6 +10,7 @@ import { ElementRef } from '@angular/core';
 import { HttpResourceOptions } from '@angular/common/http';
 import { HttpResourceRequest } from '@angular/common/http';
 import * as i0 from '@angular/core';
+import { InjectionToken } from '@angular/core';
 import { Injector } from '@angular/core';
 import { InputSignal } from '@angular/core';
 import { ModelSignal } from '@angular/core';
@@ -64,6 +65,9 @@ export interface ChildFieldContext<TValue> extends RootFieldContext<TValue> {
     readonly key: Signal<string>;
 }
 
+// @public
+export const CONTROL: InjectionToken<Control<unknown>>;
+
 // @public
 export class Control<T> {
     get cva(): ControlValueAccessor | undefined;

packages/forms/signals/src/api/control_directive.ts

@@ -15,6 +15,7 @@ import {
   ElementRef,
   EventEmitter,
   inject,
+  InjectionToken,
   Injector,
   Input,
   InputSignal,
@@ -41,6 +42,13 @@ import {FormCheckboxControl, FormUiControl, FormValueControl} from './control';
 import {AggregateProperty, MAX, MAX_LENGTH, MIN, MIN_LENGTH, PATTERN, REQUIRED} from './property';
 import type {Field} from './types';
 
+/**
+ * Lightweight DI token provided by the {@link Control} directive.
+ */
+export const CONTROL = new InjectionToken<Control<unknown>>(
+  typeof ngDevMode !== undefined && ngDevMode ? 'CONTROL' : '',
+);
+
 /**
  * Binds a form `Field` to a UI control that edits it. A UI control can be one of several things:
  * 1. A native HTML input or textarea
@@ -66,6 +74,10 @@ import type {Field} from './types';
       provide: NgControl,
       useFactory: () => inject(Control).ngControl,
     },
+    {
+      provide: CONTROL,
+      useExisting: Control,
+    },
   ],
 })
 export class Control<T> {