Switch to wp_content_img_tag filter for Improved Image Handling

[b1ink0]

Summary

Fixes #1259

Relevant technical choices

This PR updates the image processing approach by transitioning from the use of the the_content filter to the wp_content_img_tag filter.

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Co-authored-by: b1ink0 <b1ink0@git.wordpress.org>
Co-authored-by: felixarntz <flixos90@git.wordpress.org>
Co-authored-by: adamsilverstein <adamsilverstein@git.wordpress.org>
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[felixarntz]

@b1ink0 Thanks for the PR! Looks almost good to go to me, only a few points on the new function.

[felixarntz]

This really is a new function as it is incompatible with the old function signature. So we should mark it as such, it's more than a change to the existing function.

[felixarntz]

Since the signature is already not compatible with the old function, we can also come up with a better name given the different usage. For example webp_uploads_filter_image_tag().

[adamsilverstein]

Looks good, thanks! +1 to renaming suggested by Felix.

[adamsilverstein]

Nice work!