[native] Move VideoPlaybackModal close button to top right

Summary: Moved close button to top right to be more "reachable" on large devices and to be consistent with ImageModal

Test Plan: NA, here's what it looks like: https://blob.sh/atul/33d5.png

Reviewers: ashoat, palys-swm

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian, subnub, karol-bisztyga

Differential Revision: https://phabricator.ashoat.com/D800