This control has a MouseArea in it to handle scrolls, but this means that the underlying TextInput control's mouse-based behaviors get overridden and have to be re-implemented. We did this already for the cursor shape; we need to do the same for double-click-to-select-all. This commit does that.
BUG: 444348 FIXED-IN: 5.88
cc @ndavis
Testable with the panel height/width spinbox.