This commit implements a new behaviour for the "Add Driver" functionality
(invoked from the RMB menu on a property, or by pressing Ctrl-D).
Instead of spawning a context menu asking you to pick the way
you want to create a driver, it will now just create a driver on the
property under the mouse and then show the "Edit Drivers" popover so
that you can immediately start editing the properties of this driver.
This way, the whole process is more visual and feels less blocking /
constrained, with less upfront decisions needed immediately.
Notes:
* The new behaviour is equivalent to choosing the "Manually Create (Single)"
and then doing a "Edit Driver" on the property
* Renamed the old "ANIM_OT_driver_button_add" operator to
"ANIM_OT_driver_button_add_menu". It will probably go away
in the near future, but it's better to keep it around for a
while longer still until the new workflow settles down.
4605e57b0f