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

Issue number: resolves #27470

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## 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

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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. -->

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

packages/react/test/base/src/App.tsx

@@ -32,6 +32,7 @@ import IonModalConditionalSibling from './pages/overlay-components/IonModalCondi
 import IonModalConditional from './pages/overlay-components/IonModalConditional';
 import IonModalDatetimeButton from './pages/overlay-components/IonModalDatetimeButton';
 import IonPopoverNested from './pages/overlay-components/IonPopoverNested';
+import IonModalMultipleChildren from './pages/overlay-components/IonModalMultipleChildren';
 
 setupIonicReact();
 
@@ -52,6 +53,10 @@ const App: React.FC = () => (
           path="/overlay-components/modal-datetime-button"
           component={IonModalDatetimeButton}
         />
+        <Route
+          path="/overlay-components/modal-multiple-children"
+          component={IonModalMultipleChildren}
+        />
         <Route path="/keep-contents-mounted" component={KeepContentsMounted} />
         <Route path="/navigation" component={NavComponent} />
         <Route path="/tabs" component={Tabs} />