To reproduce:

1. Create an animation for an object
2. Try adding a property.
3. Observe, that if a property's name is long, you have to scroll horizontally to add it

Expected: double clicking the property should add that property. There shouldn't be a need to press a button that's is usually hidden.

Reproduced in 2017.1.4p2, 2017.2.3p2, 2017.3.2f1, 2017.4.6f1, 2018.1.7f1, 2018.2.0b11, 2018.3.0a4