feat: export TabBarIndicator

[donth77]

Motivation

Currently it’s possible to import TabBar and use the component as the tab bar in renderTabBar

import { TabBar } from 'react-native-tab-view';
 
...
 
<TabView
  renderTabBar={props => <TabBar {...props} />}
  ...
/>

Similarly it should also be possible to import TabBarIndicator so it can be used in renderIndicator.

import { TabBarIndicator } from 'react-native-tab-view';
 
...
 
<TabBar
  renderIndicator ={props => <TabBarIndicator {...props} />}
  ...
/>

I was attempting to modify the styles of the default indicator and realized that I couldn't import the component like this.

Test plan

For testing, ensure that the import statement doesn't introduce any errors.

[satya164]

Thanks for the PR!