Stop using the PNG format for HEIC thumbnails

[tmysik]

Steps to reproduce

1. enable preview for HEIC files (use the latest Imagick, install php-imagick and enable preview in the config, enabled by default)
2. upload a HEIC file (photo)
3. access this file via your web browser
4. its preview(s) is (are) generated, in the PNG (!) format

Expected behaviour

The preview image(s) should not be created in the PNG format, since this format is not usable for photos at all. In my case, the preview files occupy even more space than the original, large photos themselves (20 GB vs. 19 GB). It seems to me that the e.g. the JPG format would be much more suitable.

Actual behaviour

Thumbnails of any HEIC file/photo are generated in the PNG format.

Note: The reason is that the HEIC.php file that generates these thumbnails extends the Bitmap class which uses only the PNG format and cannot be configured to any other file type easily.

Thank you.