fix(angular): inputs on standalone form controls are reactive (#28434)

Issue number: resolves #28431

---------

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->

My previous attempt at fixing
https://github.com/ionic-team/ionic-framework/issues/28358 caused inputs
to no longer be correctly proxied to the underlying components. This was
an attempt to work around an underlying ng-packagr bug (see linked
thread for more info).

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

I decided it would be best to continue using `ProxyCmp` (since we know
that works) and find an alternative to working around the ng-packagr
bug. I spoke with the Angular team, and they recommended pulling the
provider into its own object. `forwardRef` is now required since we are
referencing the component before it is declared.

- Revert
82d6309ef1
- Moves provider to an object to avoid ng-packagr issue
- I reverted the proxy e2e tests. These are no longer needed since we
are not ejecting from the typical `ProxyCmp` usage anymore.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->
Dev build: `7.5.3-dev.11698699090.1151d73f`
Verified that the issue is fixed with the repro provided in
https://github.com/ionic-team/ionic-framework/issues/28431

Also verified that this does not regress the issue described in
https://github.com/ionic-team/ionic-framework/issues/28358.

packages/angular/standalone/src/directives/checkbox.ts

@@ -7,26 +7,14 @@ import {
   HostListener,
   Injector,
   NgZone,
+  forwardRef,
 } from '@angular/core';
-import type { OnInit } from '@angular/core';
 import { NG_VALUE_ACCESSOR } from '@angular/forms';
 import { ValueAccessor, setIonicClasses } from '@ionic/angular/common';
 import type { CheckboxChangeEventDetail, Components } from '@ionic/core/components';
 import { defineCustomElement } from '@ionic/core/components/ion-checkbox.js';
 
-/**
- * Value accessor components should not use ProxyCmp
- * and should call defineCustomElement and proxyInputs
- * manually instead. Using both the @ProxyCmp and @Component
- * decorators and useExisting (where useExisting refers to the
- * class) causes ng-packagr to output multiple component variables
- * which breaks treeshaking.
- * For example, the following would be generated:
- * let IonCheckbox = IonCheckbox_1 = class IonCheckbox extends ValueAccessor {
- * Instead, we want only want the class generated:
- * class IonCheckbox extends ValueAccessor {
- */
-import { proxyInputs, proxyOutputs } from './angular-component-lib/utils';
+import { ProxyCmp, proxyOutputs } from './angular-component-lib/utils';
 
 const CHECKBOX_INPUTS = [
   'checked',
@@ -41,40 +29,42 @@ const CHECKBOX_INPUTS = [
   'value',
 ];
 
+/**
+ * Pulling the provider into an object and using PURE works
+ * around an ng-packagr issue that causes
+ * components with multiple decorators and
+ * a provider to be re-assigned. This re-assignment
+ * is not supported by Webpack and causes treeshaking
+ * to not work on these kinds of components.
+ */
+const accessorProvider = {
+  provide: NG_VALUE_ACCESSOR,
+  useExisting: /*@__PURE__*/ forwardRef(() => IonCheckbox),
+  multi: true,
+};
+
+@ProxyCmp({
+  defineCustomElementFn: defineCustomElement,
+  inputs: CHECKBOX_INPUTS,
+})
 @Component({
   selector: 'ion-checkbox',
   changeDetection: ChangeDetectionStrategy.OnPush,
   template: '<ng-content></ng-content>',
   // eslint-disable-next-line @angular-eslint/no-inputs-metadata-property
   inputs: CHECKBOX_INPUTS,
-  providers: [
-    {
-      provide: NG_VALUE_ACCESSOR,
-      useExisting: IonCheckbox,
-      multi: true,
-    },
-  ],
+  providers: [accessorProvider],
   standalone: true,
 })
-export class IonCheckbox extends ValueAccessor implements OnInit {
+export class IonCheckbox extends ValueAccessor {
   protected el: HTMLElement;
   constructor(c: ChangeDetectorRef, r: ElementRef, protected z: NgZone, injector: Injector) {
     super(injector, r);
-    defineCustomElement();
     c.detach();
     this.el = r.nativeElement;
     proxyOutputs(this, this.el, ['ionChange', 'ionFocus', 'ionBlur']);
   }
 
-  ngOnInit(): void {
-    /**
-     * Data-bound input properties are set
-     * by Angular after the constructor, so
-     * we need to run the proxy in ngOnInit.
-     */
-    proxyInputs(IonCheckbox, CHECKBOX_INPUTS);
-  }
-
   writeValue(value: boolean): void {
     this.elementRef.nativeElement.checked = this.lastValue = value;
     setIonicClasses(this.elementRef);