image-source: Move checkboxes to playback mode setting

[derrod]

Description

Changes image slideshow properties to use a combobox (displayed as radio buttons) for the playback mode to make it more obvious that "randomize" and "loop" are mutually exclusive.

Motivation and Context

Users get confused, e.g. #9342

How Has This Been Tested?

Checked that settings get set and migrated correctly.

Types of changes

• Tweak (non-breaking change to improve existing functionality)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.

[derrod]

Also needs to be updated now that #10088

[derrod]

Updated for Mk.2 and changed to use a combobox instead of radio buttons.

[cg2121]

I still have a couple of problems with this:

• Shuffle and random are two completely different things
• Shuffling is reordering the list of images in a random order, and they can only be shown once when going through the list of images
• Random is picking a image randomly out of the list, and in theory the same image could be used twice in a row
• It should be like the VLC source where it uses a shuffle and has the ability to loop independent of that
• The slideshow source currently uses random selection and not shuffle

[derrod]

Renamed back to "Random" because that's what it is.