Issue number: N/A

---------

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

As mentioned in this
[PR](ionic-team/ionic-docs#3797), React
`IonTabs` requires `IonTabBar` do be a child, else it doesn't render and
throws an error.

Angular, JS, and Vue doesn't have this requirement.

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

I didn't see any reason why React does not mimic the other frameworks.
In order to keep consistency, I've updated the React tabs. This would
allow `ion-tabs` and `ion-tab-bar` can be used as standalone elements as
mentioned in the [docs](https://ionicframework.com/docs/api/tabs).

- React follows the same structure as the other frameworks: `IonTabs`
doesn't require `IonTabBar` to be a child to render.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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## Other information

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

Dev build: 8.3.1-dev.11726159792.1a6f49de

How to test:
1. Create a Ionic React app through the Ionic CLI with tabs as the
starter
2. Run the app
3. Comment out the `IonTabBar`
4. Notice that the `IonTabs` does not render
5. Notice that there's an error in the console: "IonTabs needs a
IonTabBar"
6. Install the dev build: `npm install
@ionic/[email protected]`
7. Make sure the `IonTabBar` is still commented out
8. Verify that `IonTabs` renders
9. Verify that there isn't an error in the console