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

Issue number: resolves #27470

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## What is the current behavior?
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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:
https://github.com/ionic-team/ionic-framework/blob/eb2772c0ce623de70cce42b5d36e86cdbba7bafb/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`:
https://github.com/ionic-team/ionic-framework/blob/eb2772c0ce623de70cce42b5d36e86cdbba7bafb/angular/src/directives/overlays/modal.ts#L82

## What is the new behavior?
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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