Tooltips not shown anymore for comboboxes in text toolbar

Tooltips are not shown anymore for the comboboxes (dropdowns) of the text toolbar.

Likely cause by the recent refactoring (see 346e7643).

Inkscape Version and Operating System:

• Inkscape Version: Inkscape 1.0alpha2 (83e8a34c, 2019-06-05
• Operating System: Windows 10