[native] Add spinner to VideoPlaybackModal
[native] Add spinner to VideoPlaybackModal

Summary: Spinner displayed until `onReadyForDisplay` callback

Test Plan: Works as expected on iOS. Will test android and media pipeline scenarios comprehensively after the native video playback diffs.

Reviewers: ashoat, palys-swm

Reviewed By: ashoat

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

Differential Revision: https://phabricator.ashoat.com/D799

Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal,Ashoat/squadcal