Menu action tooltips don't show

[jonathanrocher]

When running the examples/tasks/advanced/run.py, even after adding tooltips to TaskActions, these tooltips don't appear on hover on the menu. For Qt>5.1, they should per this. Marking this as a bug since Action objects have tooltip attribute but they don't show up when set. It aguably could be an enhancement too.

Per https://stackoverflow.com/questions/21725119/why-wont-qtooltips-appear-on-qactions-within-a-qmenu, apparently, 2 things must happen:

• The QAction must call setToolTip which I believe is done here
• The QMenu must call setToolTipsVisible(True) which I think is missing from the _Menu class (https://github.com/enthought/pyface/blob/master/pyface/ui/qt4/action/menu_manager.py).

Seen with python 3.6 on current master on OSX (w/ traitsui 7.0.1-1, traits 6.1.0-1, qt 5.12.6-5, pyqt5 5.14.2-3).

[corranwebster]

We want to be a little careful with this:

• we are still supporting Qt4.8, so we have to be careful with code paths
• different OS have different conventions about tooltips for menus: it isn't common on MacOS, for example, but is more common on Windows. We may want to set different default behaviour based on the OS.