Expand UI Tester Range Editor implementation

As mentioned here: https://github.com/enthought/traitsui/pull/1171#discussion_r480143531 we will want to include an implementation for SimpleSpinEditor
This will require additional solvers and potentially special handling of the SpinBox/SpinCtrl object.

Additionally, we will want to add the functionality for locating and interacting with a slider, and for clicking on any buttons (e.g. in the SimpleSpin Editor or LargeRangeSliderEditor)