Closes #504 AVIF support

[Tabrisrp]

Description

Add AVIF support in the plugin

Closes #504

Documentation

User documentation

Explain how this code impacts users.

Technical documentation

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Type of change

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• New feature (non-breaking change which adds functionality).
• Bug fix (non-breaking change which fixes an issue).
• Enhancement (non-breaking change which improves an existing functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as before).

New dependencies

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Risks

List possible performance & security issues or risks, and explain how they have been mitigated.

Checklists

Feature validation

• I validated all the Acceptance Criteria. If possible, provide sreenshots or videos.
• I triggered all changed lines of code at least once without new errors/warnings/notices.
• I implemented built-in tests to cover the new/changed code.

Documentation

• I prepared the user documentation for the feature/enhancement and shared it in the PR or the GitHub issue.
• The user documentation covers new/changed entry points (endpoints, WP hooks, configuration files, ...).
• I prepared the technical documentation if needed, and shared it in the PR or the GitHub issue.

Code style

• I wrote self-explanatory code about what it does.
• I wrote comments to explain why it does it.
• I named variables and functions explicitely.
• I protected entry points against unexpected inputs.
• I did not introduce unecessary complexity.
• I listed the introduced external dependencies explicitely on the PR.
• I validated the repo-specific guidelines from CONTRIBUTING.md.

Observability

• I handled errors when needed.
•  I wrote user-facing messages that are understandable and provide actionable feedbacks.
• I prepared ways to observe the implemented system (logs, data, etc.).

Risks

•  I explicitely mentioned performance risks in the PR.
• I explicitely mentioned security risks in the PR.

[Mai-Saad]

Notes [WIP]:
1- Bulk optimization notice displayed when enable/disable create AVIF (When enable AVIF, despite of having 4 images in media library, AVIF was created for single image and media progress was stuck at 50% till we reoptimize any image, it will stop . @piotrbak is there any need to show progress in bulk optimization once enable AVIF?) => on trunk, was only displayed when click bulk optimization
Recommendation:

• no need for bulk optimization notice as we are only generating AVIF and not re-optimizing all images
• even if we agreed to display the notice, it shouldn't be on plugins/post/users... pages

[Mai-Saad]

Related initial test plan https://wpmediaqa.testrail.io/index.php?/runs/view/820&group_by=cases:section_id&group_order=asc

[Mai-Saad]

Working as expected with the following notes:

• With latest WP nighty version, if we uploaded avif , in media library it is mentioned as not supported => possible enhancement may be at core to have thumbnail for this image as same as with webP , while on our side , optimizing this image as same as when uploading webp
• Avif isnot created for gif nor webp images (gif have separate GH)
• Generate missing next-gen images count may be -ve or invalid in some cases
• Disable avif won't generate webp by default for existing images although generating next-gen will be loading in settings
• Displayed size in media library is always webp if it exists while avif is there (have separate GH)
• The missing next-gen count not handling the case when both avif and webp are on (in this case it will count only avif)
  testrail-report-580.pdf