- Ensure that the modified-warning won't be displayed, when navigating away from the viewer, if the user has added custom Annotations and then *removed all* of them.
- Ensure that the *initial* editor-buttons state, i.e. the `toggled`-class, is correctly displayed in the toolbar when then viewer loads.
- Tweak the CSS-classes for the editor-buttons, such that they use the correct focus/hover-rules (similar to the sidebar-buttons).
- Remove a no longer accurate comment from the `BaseViewer.annotationEditorMode`-setter.
- Address a couple of *smaller* outstanding review comments, including some re-formatting changes, from PR 14976.
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