fix(overlays): assign incremental id to overlay host (#27278)

Issue number: Internal

---------

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

The counter for incrementing the `id` and `z-index` of an overlay is
incremented whenever the `connectedCallback` is fired for an overlay.

When an overlay is presented and/or conditionally rendered, the overlay
`id` can increment by `n+2` instead of `n+1`.

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

- Increments all overlay ids consistently
- Removes legacy `ion-modal-{id}` and `ion-popover-{id}` logic
- Adds unit tests for the id behavior
- Tests are split up into separate files so that the counter is always
starting from `0`
- Adds an integration test with the Angular test app to verify
conditional rendering behavior

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->

core/src/components/alert/alert.tsx

@@ -17,6 +17,7 @@ import {
   prepareOverlay,
   present,
   safeCall,
+  setOverlayId,
 } from '../../utils/overlays';
 import type { OverlayEventDetail } from '../../utils/overlays-interface';
 import type { IonicSafeString } from '../../utils/sanitization';
@@ -329,6 +330,7 @@ export class Alert implements ComponentInterface, OverlayInterface {
   }
 
   componentWillLoad() {
+    setOverlayId(this.el);
     this.inputsChanged();
     this.buttonsChanged();
   }

core/src/components/alert/test/alert-id.spec.ts

@@ -0,0 +1,41 @@
+import { newSpecPage } from '@stencil/core/testing';
+
+import { Alert } from '../alert';
+
+it('alert should be assigned an incrementing id', async () => {
+  const page = await newSpecPage({
+    components: [Alert],
+    html: `<ion-alert is-open="true"></ion-alert>`,
+  });
+  let alert: HTMLIonAlertElement;
+
+  alert = page.body.querySelector('ion-alert')!;
+
+  expect(alert).not.toBe(null);
+  expect(alert.getAttribute('id')).toBe('ion-overlay-1');
+
+  // Remove the alert from the DOM
+  alert.remove();
+  await page.waitForChanges();
+
+  // Create a new alert to verify the id is incremented
+  alert = document.createElement('ion-alert');
+  alert.isOpen = true;
+  page.body.appendChild(alert);
+  await page.waitForChanges();
+
+  alert = page.body.querySelector('ion-alert')!;
+
+  expect(alert.getAttribute('id')).toBe('ion-overlay-2');
+
+  // Presenting the same alert again should reuse the existing id
+
+  alert.isOpen = false;
+  await page.waitForChanges();
+  alert.isOpen = true;
+  await page.waitForChanges();
+
+  alert = page.body.querySelector('ion-alert')!;
+
+  expect(alert.getAttribute('id')).toBe('ion-overlay-2');
+});