We already have the `description` property on panels but are currently not
displaying it when hovering over a panel header. With this patch, the
descriptions will be shown in group nodes as well as the geometry nodes
modifier.
I had to do two lower level changes for layout panels because it didn't work
with tooltips properly.
* Tooltips make the label in the panel header interactive, but clicking to
open/close the panel should still work.
* The tooltip should disappear when clicking on the header. This is consistent
with tooltips in other places.
Pull Request: https://projects.blender.org/blender/blender/pulls/127852
c0179a1b78