refactor(core): add utility type for extracting the value of a custom control

Adds the `ɵExtractFormControlValue` type that we can use during template type checking to extract the type of a custom control.

(cherry picked from commit 4b68bddd62)

packages/compiler/src/render3/r3_identifiers.ts

@@ -494,6 +494,7 @@ export class Identifiers {
   // type-checking
   static InputSignalBrandWriteType = {name: 'ɵINPUT_SIGNAL_BRAND_WRITE_TYPE', moduleName: CORE};
   static UnwrapDirectiveSignalInputs = {name: 'ɵUnwrapDirectiveSignalInputs', moduleName: CORE};
+  static ExtractFormControlValue = {name: 'ɵExtractFormControlValue', moduleName: CORE};
   static unwrapWritableSignal = {name: 'ɵunwrapWritableSignal', moduleName: CORE};
   static assertType = {name: 'ɵassertType', moduleName: CORE};
 }

packages/core/src/core_render3_private_export.ts

@@ -95,6 +95,7 @@ export {
   ɵɵcontentQuerySignal,
   ɵɵcontrol,
   ɵɵcontrolCreate,
+  ɵExtractFormControlValue,
   ɵɵcomponentInstance,
   ɵɵCopyDefinitionFeature,
   ɵɵdefineComponent,

packages/core/src/render3/index.ts

@@ -97,6 +97,7 @@ export {
   ɵɵproperty,
   ɵɵcontrol,
   ɵɵcontrolCreate,
+  ɵExtractFormControlValue,
   ɵɵcontentQuery,
   ɵɵcontentQuerySignal,
   ɵɵloadQuery,

packages/core/src/render3/instructions/control.ts

@@ -32,6 +32,18 @@ import {listenToOutput} from '../view/directive_outputs';
 import {listenToDomEvent, wrapListener} from '../view/listeners';
 import {setPropertyAndInputs, storePropertyBindingMetadata} from './shared';
 import {writeToDirectiveInput} from './write_to_directive_input';
+import {ModelSignal} from '../../authoring/model/model_signal';
+
+/**
+ * Used during template type checking to extract the type of a custom form control.
+ *
+ * @codeGenApi
+ */
+export type ɵExtractFormControlValue<T> = T extends {value: ModelSignal<infer V>}
+  ? V
+  : T extends {checked: ModelSignal<boolean>}
+    ? boolean
+    : unknown;
 
 /**
  * Possibly sets up a {@link ɵControl} to manage a native or custom form control.

packages/core/test/render3/jit_environment_spec.ts

@@ -38,6 +38,7 @@ const AOT_ONLY = new Set<string>([
 
   // used in type-checking.
   'ɵINPUT_SIGNAL_BRAND_WRITE_TYPE',
+  'ɵExtractFormControlValue',
   'ɵUnwrapDirectiveSignalInputs',
   'ɵunwrapWritableSignal',
   'ɵassertType',