fix(react, vue): inline modals apply ion-page class (#27481)

Issue number: resolves #27470

---------

<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->

<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->

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

Passing multiple elements in to an inline modal causes `.ion-page` to
not get set. This causes content to get pushed off the bottom of the
modal equal to the height of the header. React has some special CSS that
prevents this:
eb2772c0ce/packages/react/src/components/createInlineOverlayComponent.tsx (L137-L140)

However, I think this should be delegated to `.ion-page` instead so the
behavior is consistent across frameworks. For example, Angular uses
`.ion-page`:
eb2772c0ce/angular/src/directives/overlays/modal.ts (L82)

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

- Inline overlays in Ionic React and Ionic Vue wrap child content in
`.ion-delegate-host.ion-page`.
- Removed the custom flex styles from Ionic React as `.ion-page` has its
own styles.

## 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

<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->

Revised Design Doc:
https://github.com/ionic-team/ionic-framework-design-documents/pull/84

packages/vue/test/base/src/router/index.ts

@@ -29,6 +29,10 @@ const routes: Array<RouteRecordRaw> = [
     path: '/overlays',
     component: () => import('@/views/Overlays.vue')
   },
+  {
+    path: '/modal-multiple-children',
+    component: () => import('@/views/ModalMultipleChildren.vue')
+  },
   {
     path: '/keep-contents-mounted',
     component: () => import('@/views/OverlaysKeepContentsMounted.vue')

packages/vue/test/base/src/views/ModalMultipleChildren.vue

@@ -0,0 +1,16 @@
+<template>
+  <ion-page data-pageid="modal-multiple-children">
+    <ion-content class="ion-padding" :fullscreen="true">
+      <ion-button id="show-modal">Show Modal</ion-button>
+
+      <ion-modal trigger="show-modal">
+        <div class="child-content">Content A</div>
+        <div class="child-content">Content B</div>
+      </ion-modal>
+    </ion-content>
+  </ion-page>
+</template>
+
+<script setup lang="ts">
+import { IonButton, IonContent, IonPage, IonModal } from '@ionic/vue';
+</script>