Transparency lost when cropping/resizing images

[SharkyKZ]

Closes #30975.

Summary of Changes

Fixes transparency being lost when cropping/resizing PNG images.

Testing Instructions

Go to edit template files in backend.
Select one of PNG images in images directory.
Use Crop and Resize buttons to crop/resize the image.

Note, because template is styled to have a black background behind transparent images, you'll have to inspect image files directly on your server or in the browser.

Actual result BEFORE applying this Pull Request

Transparency is lost, images get a black background.

Expected result AFTER applying this Pull Request

Images maintain transparency.

Documentation Changes Required

No.

[Quy]

I have tested this item ✅ successfully on df6c803

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[ghost]

I have tested this item ✅ successfully on df6c803

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[alikon]

RTC

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[HLeithner]

Don't we support other types like webp?

[SharkyKZ]

No.

[HLeithner]

Thanks