Fix active state overlay in content editor

What does this MR do and why?

In content editor toolbars (top toolbar and contextual), fix overlapping active states.

See: #406721 (closed)

Screenshots or screen recordings

Before	After
	Main toolbar Code block bubble menu Formatting bubble menu

How to set up and validate locally

1. Access content editor. Content editor (rich text editor) is available in wikis globally, and in issue/MR comments behind a feature flag :content_editor_on_issues. Click "Viewing markdown" at bottom right and select "Rich text" from the menu to switch to content editor.
2. Use B/I/S on any selected text.
3. Notice that the toolbar active states no longer overlap.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.