KeyboardAvoider: Make more explicit for clearer types.
KeyboardAvoider: Make more explicit for clearer types.

Fixes two Flow errors (with Flow 0.75) that warn of unused props.
For one platform we use `KeyboardAvoidingView` for the other
we use a simple `View`. The latter does not have a `behavior`
property, nor `contentContainerStyle`.

vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile,vishwesh3/zulip-mobile