Replaces `Space Image` drop-box with a file handler in order to support
opening multiple sets of files at once and to allow users to add their
own file handler to the Image editor space if desired.
A new `Image_OT_open_images` operator is introduced that uses
`Image_OT_open` internally. It groups files by different sequences and
UDIMs and loads each group accordingly.
Co-authored-by: Jesse Yurkovich <deadpin>
Pull Request: https://projects.blender.org/blender/blender/pulls/117707
b97ac126f8