Make custom tooltips use the same system as the built-in tooltip system#3094

By default, TTS supports tooltips when hovering over objects, showing the title and afther a few seconds the description of the object. When using a custom tooltip however (such as with XML buttons), the tooltip is ‘attached’ to the XML object and not to the cursor like the built-in system. Although I can set the fontsize, I need to zoom in on the table to actually read the text. Of course I can set the fontsize to enormous, but a more elegant solution would be to enable showing custom tooltips using the built-in system to show in just above the cursor. That fontsize is readable no matter how far I’m zoomed in/out on the table.