[UX] CKEditor configuration: Add a label to the "button separator" button

[klonos]

Backdrop:

D8:

Tooltips do not work on devices with touch screens, so we should add a label to this button.

[klonos]

I have tried to take a stab at this, but the "Button separator" button seems to be rendered as part of a "multiple buttons" group (which are buttons that can be placed multiple times in the CKEditor toolbar). Right now, this button is the only button in that group, so adding a "Button separator" label as a span to the entire group does work visually, but it is not future-proof. In other words, when/if more such "multiple buttons" are added in the future, the label needs to apply to all of them; not just the separator.

So, if we add the label to the button, it will look like so:

...and if we add it to the group, it'll look like so:

So, do we special-case the separator button and move it out of the "multiple buttons" group, into its own group? Do we add multiple "multiple buttons" groups and keep one only for the separator button? ...or do we add the label to the button (which IMO does not look good visually)?

Thoughts?

[klonos]

...the solution to this problem would be very simple, if the answer to the following question is yes:

Is it safe to assume that the button separator is the only button that will ever be a "multiple button"?