Missing explanation for return values from Tween methods

[snoopdouglas]

Your Godot version:
3.3.2

Issue description:
Tween's interpolate_property and start methods return bools, but there's no explanation in the docs for what they mean.

They always seem to return true whenever I use them, but in order to avoid a warning I need to capture the value for an assert or something, so it'd be good to know for sure that true is what I should expect on success - if that is indeed the case.

URL to the documentation page:
https://docs.godotengine.org/en/stable/classes/class_tween.html

[timothyqiu]

They return false if the requested operation can't be completed successfully. For example, when trying to start the tween before being added to the scene tree, or any of the parameters does not make sense (e.g. when object is null for interpolate_* methods).

... and these methods are all changed to return nothing in 4.0 in godotengine/godot#36844 🤣

[akien-mga]

Fixed by godotengine/godot#56639.