[editor] A couple of small FreeText-related fixes (PR 14976 follow-up)

- 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.

web/l10n_utils.js

@@ -81,6 +81,7 @@ const DEFAULT_L10N_STRINGS = {
   printing_not_ready: "Warning: The PDF is not fully loaded for printing.",
   web_fonts_disabled:
     "Web fonts are disabled: unable to use embedded PDF fonts.",
+
   freetext_default_content: "Enter some text…",
 };