Image Block: Show snackbar error notice when HEIC image is added

[AhmarZaidi]

Fixes part of: #66293

What?

This PR adds a 'snackbar' error notice for HEIC image uploads.

Why?

When an HEIC file is uploaded to a server that does not support HEIC to JPEG conversion, and the browser (such as Chrome or Firefox) does not support displaying HEIC, users see the alt text 'This image has an empty alt attribute; its file name is ...', however if we upload an HEIC image from the Media Library.

How?

Added an error notice of type 'snackbar' on image error after checking if the uploaded image is HEIC type.

Testing Instructions

1. Open a post or page in the WordPress editor.
2. Add a core/image block.
3. Upload an HEIC image file.
4. Observe the error notice that appears, which should include the filename and a suggestion to convert the image to JPEG.

Testing Instructions for Keyboard

N/A

Screenshots or screencast

Screen.Recording.2024-10-23.at.5.11.51.PM.mov

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Co-authored-by: AhmarZaidi <ahmarzaidi@git.wordpress.org>
Co-authored-by: adamsilverstein <adamsilverstein@git.wordpress.org>
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[adamsilverstein]

Instead of adding a warning notice, we should probably prevent users from uploading .heic files if their server doesn't support conversion into a web-safe format like jpeg.

[adamsilverstein]

WordPress automatically does this conversion for uploaded HEICs when the server supports it.

[ironprogrammer]

Thanks for the PR, @AhmarZaidi! Though I agree with Adam's comment that preventing [future] HEIC uploads on an unsupported server would be preferable goal. This snackbar would have been a great addition if part of 6.7. However, by the time this update would ship in Core with 6.8, it's likely that it will be more difficult for users to get into this situation.

#66293 is more about warning users that their existing inserted HEIC image is problematic. The placeholder itself looks wonky and doesn't clarify that most users won't be able to view the image.