fix(tabs): use relative fragment manager

[edusperoni]

@farfromrefug we were unsure this fix was needed, but apparently it is, as tabs break on modal pages

[farfromrefug]

@edusperoni what bugs me is that i think it was changed to Root before because it was creating an issue :s
i am not sure what to do. Maybe we should at least create more sample in the demo app (not sure which one) to ensure we can test all cases when we make changes like this? (not asking to do it for this PR)

[edusperoni]

I was talking to @NathanWalker about it some time ago and I believe we need some kind of integration testing with NativeScript core and the material components overall, considering tabs and botom nav are part of the template projects. Still wondering how exactly we should do it, but I definitely see your point.

That fix on BottomNavigation actually fixed a lot of stuff on our many prod projects, so maybe something changed since your last try?

[farfromrefug]

@edusperoni yes i dont know i would say that change dates from before the migration to this repo but i am 1000% sure.
we could get some detox tests set-up. Though i am really not the best with tests :P

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