Add support for Bezier animation tracks

[lpszmoths]

Repro steps

1. Create a new scene starting from an empty Spatial root node
2. Add a Spatial node and rename it ModifiersTarget
3. Add and configure the Modifiers node
   3.1. Add a Modifiers node and rename it Modifiers
   3.2. In the Modifiers inspector, set ModifiersTarget as the target of Modifiers
   3.3. In the Modifiers inspector, click on Add Property
   3.4. Select the Transform property
   3.5. Click on Add Modifier
   3.6. Name the new modifier TargetTransform
4. Animation player setup
   4.1. Add an AnimationPlayer to the scene
   4.2. Create a new animation named Scale
   4.3. Open the animation bottom panel and click on Add Track
   4.4. Select Bezier Curve Track
   4.5. Select the Modifiers node.

Actual result

The modifier we created does not appear on the list, so I can't animate it with a Bezier track.

Expected result

When you create a new Bezier curve track, you should be able to see Modifiers nodes, select their modifiers, and animate them.

I haven't taken a look at the code so I'm not sure if this is dependent on godotengine/godot-proposals#300

Otherwise great plugin!

[samdze]

I'll take a look, may be a Godot bug.

[samdze]

Alright, I see, it's not that the Modifiers plugin doesn't support Bezier animation tracks, It's Bezier tracks that don't support the Transform type, of course.

The default editor property selector shows extra properties for Spatial nodes (and other types of nodes too).
Right now the plugin shows non-computed properties only, but I'll update it so that the property selector also shows those extra ones!

[samdze]

Fixed by 3d2c222