Regression in D1812: PyDriver variables as Objects
Taking the Python representation is nice in general
but for enums it would convert them into strings,
breaking some existing drivers.
Drivers can use this to refer to the data which the driver is applied to,
useful for objects, bones, to avoid having to create a variable pointing to its self.
Support for driver variables that don't resolve to numbers, eg:
objects, bones, curves... etc.
Without this, Python expressions to access this data needed to use an absolute path from `bpy.data`,
however this is inconvenient, breaks easily (based on naming) and wouldn't set the dependencies correctly.
