Font collections improvements

• Fix delete not working either on the font collections or their fonts in the Font Collections dialog.

• Fix font list not updating when updating a font in the currently selected font collections (Synchronization problems).

• Fonts will no longer appear grey in the Font Collections dialog.

• Collection rename improvements:

  • Expanded font collections no longer collapses.
  • Prevent empty entry from being created in the font collection dialog.
  • Preserves selection: If the rename is success, selects the updated name.

• Replaced default drag & drop position indicators with more intuitive ones.

• Moved the Clear all filters button into the font collections popup in the Text and Font dialog.

• Removed system font collections from the Font Collections dialog, as they are not user-editable.

• Added font count column in the Font Collections dialog for improved feedback during font add and delete operations.

• Minor tweaks in the layout for improved UX.

• Browsing fonts no longer triggers unnecessary additions to the recently used fonts list.

• The recently used fonts list is now updated during the file save operation.

• Connected the unified font browser to the font collections' connect_update signal to ensure the font collections are updated in the filter popover whenever the user makes any changes.

Fixes: #4196 Fixes: #4188 (closed)