fix/workaround: iOS video thumbnails in BlockVideo/BaseVideo

[stephiescastle]

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Description

Native videos in BlockVideo don't load a thumbnail on iOS. This is a workaround that ensures the first frame will be loaded.

Important notes:

A couple notable reasons we may not want to merge this "fix":

• Note that iOS's behavior may be intentional for performance reasons.
• if the video is super short, like a few seconds, the video jogger will look slightly advanced:

Instructions to test

1. Use an iphone or iphone simulator (XCode) to view BlockVideo http://localhost:6006/iframe.html?args=&globals=&id=components-blocks-blockvideo--base-story#/
2. There should be a thumbnail

Tested in the following environments/browsers:

Operating System

• macOS
• iOS
• iPadOS
• Windows

Browser

• Chrome
• Firefox ESR
• Firefox
• Safari
• Edge

[sfimbres]

LGTM!

Confirmed working on iPhone 16 simulator (Xcode)