Steps to reproduce:
1. Create a new project or open existing one
2. Select any game object in the "Hierarchy"
3. Go to Window->Animation->Animation and press Create (for creating a new animation clip)
4. Close Animation window
5. Double click "New Animation" item in "Project" tab
-Animation window doesn't open

Expected result: double-clicking animation file should open Animation window, just like double-clicking controller or timeline files open Animator and Timeline windows
Actual result: double-clicking animation file in "Project" tab does not open the Animation window

Reproduced on: 2018.1.8f1, 2018.2.0f2, 2018.3.0a6