Remove drawn features layer when geometries are cleared

[sufyanAbbasi]

• Ensures that whenever the last drawn geometry is removed, regardless of whether it was deleted from the map using the draw control tools or reset using the draw_control.reset() method, the "Drawn Features" layer will also be removed from the layers list.

See: https://colab.research.google.com/drive/1vzHVOhtEr9lQwKqPHh3CkF2FIVcQ5SLN?usp=sharing

[giswqs]

LGTM.

[naschmitz]

Could you add unit tests (as long as it doesn't take too long)?

[sufyanAbbasi]

Could you add unit tests (as long as it doesn't take too long)?

Done. To make this better testable, I refactored to move the layer deletion logic to where we call redraw_layer() in the handle_geometry_delete method, and added some more implementation details to the FakeMap.

[naschmitz]

Thank you so much!