Fix issue BottomTabs Elevation not working on Android

[vnhanh]

This issue was raised on this link: #7422

The code which sets bottomtabs elevation:
Navigation.setDefaultOptions({
statusBar: {
backgroundColor: '#4d089a'
},
topBar: {
title: {
color: 'white'
},
backButton: {
color: 'white'
},
background: {
color: '#4d089a'
}
},
bottomTab: {
fontSize: 14,
selectedFontSize: 14,
selectedTextColor: '#069A8E',
selectedIconColor: '#069A8E'
},
bottomTabs: {
titleDisplayMode: 'alwaysShow',
iconWidth: 24,
iconHeight: 24,
elevation: 8,
}
});

With the version "7.27.1", the android application doesn't show elevation like this picture:

And if using the fixing code from my branch, it will show elevation:

Please check carefully, you can see the elevation in the second picture.

[Andarius]

Hey @vnhanh, from what I understood from this issue #7476 is that the elevation is displayed under the bottomTabs and not above. Does this fix the same issue or is it another fix ?

[guyca]

Thanks a lot @vnhanh! Your effort helped me find a slightly better solution in #7519

[vnhanh]

@guyca OK, I'm glad to help everyone develop this library. Thanks for reviewing.
@Andarius My pull request fixes to show shadow on the above of the BottomTabs's top edge. I read the issue in #7746 and I think my code can fix that issue, but @guyca found a better solution, so I think you can wait more until your issue is fixed. Thanks for reading my pull request.