Trackpad scrolling doesn't work in AnimationTree's StateMachine editor

[ArdaE]

Godot version:
3.2.2 stable

OS/device including version:
macOS 10.15.6

Issue description:
The built-in trackpad of MacBook works fine in most panes of Godot, but doesn't in the AnimationTree's StateMachine editor. The trackpad works fine in AnimationTree's BlendTree editor, which is a very similar/sibling editor.

Steps to reproduce:
On a MacBook:

1. Create an AnimationTree node
2. Set AnimationTree's Tree Node property to a new AnimationNodeBlendTree
3. Use two-finger scrolling to move the pane both horizontally and vertically and verify that scrolling works fine
4. Set AnimationTree's Tree Node property to a new AnimationNodeStateMachine
5. Use two-finger scrolling again and note that neither horizontal nor vertical scrolling works (you can verify this by watching the scroll bars or by adding an arbitrary animation node to better see that the window is not scrolling)

Related issues:
There's another trackpad related issue, #38237, that affects another editor pane of Godot.