Video: Enable autoplay for video on iOS devices

[im3dabasia]

What?

Closes #41573

Why?

Video blocks with autoplay enabled fail to work properly on iOS devices. While the muted attribute is automatically added when autoplay is toggled on, iOS devices specifically require the playsinline attribute to properly autoplay videos.

The current implementation ignores this iOS-specific requirement, resulting in a poor user experience for a significant portion of users, as iOS devices represent a large market share.

How?

This PR extends the existing autoplay logic to automatically set both muted and playsinline attributes when autoplay is enabled. When a user toggles on autoplay:

1. The muted attribute is set to true (existing behavior)
2. The playsInline attribute is now also set to true (new behavior)

Additionally, I've added a help text that informs users when "Play inline" is automatically enabled due to autoplay settings.

Testing Instructions

(You'll need to use an actual iPhone or a simulator for this)

1. Create a new post or edit an existing one
2. Add a Video block and upload a video
3. Enable autoplay in the block settings
4. Preview or publish the post
5. Verify that the video automatically plays when it appears on screen (Check in iphone)

Screenshots or screencast

Before

pre_playsinline.MP4

After

post_playsinline.MP4

[github-actions]

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[t-hamano]

Sorry for the late reply. Given #69232, I think this approach makes sense 👍

Just to be sure, can you rebase this PR on top of trunk before merging?

[t-hamano]

@im3dabasia have you ever merged the approved PR yourself? I think you're already a member of the Gutenberg repo, so if you haven't already, give it a go 👍

When merging any PR, don't forget to add the props list. It would also be good to align the commit message with the PR title if there is a difference between them.