[2.2.0] UX of source selector for slots

Problem/Motivation

For beta2, we did a great work about UX.

We have only 2 issues left for extra improvment:

• #3469795: [2.2.0] Component selector: use SDC's thumbnailPath?
• #3466383: [2.0.0-beta5] Options in field formatter are cut off, impossible to know what's being selected

However, there is still a part we are not happy about: the source selector for slots.

Proposed resolution

No solution proposed here, but just a call to open our mind: anything is possible, let's brainstorm, let's be crazy.

Some ideas:

• Better naming for some sources
• Change the order of sources and the grouping of sources
• Slot the dropbutton in many dropbuttons, or a a dropbutton with normal buttons, or with only buttons
• Add icons to sources, unicode character or inline SVG, declared in the plugin class's PHP attributes
• ...