Add a note of loop_mode for custom_timeline to the NodeAnimation docs

[TokageItLab]

• Follow up Rework AnimationNode process for retrieving the semantic time info #87171

I have found that the behavior varies depending on the value of the actual Animation resource property.

However, this is an unavoidable problem due to the architecture design. I added a note to the documentation describing the cases where the problem occurs and the reasons why.

[Mickeon]

I do not understand this, either.

Also dedicating 3 lines to the same topic is excessive. Keep in mind each new line is separated into paragraphs in the class reference, that is, one more new line is added in the middle of these. This means each line tends to be roughly self-contained.
I don't like this behavior personally, as it conflicts with how GitHub Flavored Markdown does it, but it is what it is,

It should all be one line (maybe with well-placed [br] tags if it's okay to).
But still, watch out. This is an overwhelming amount of information to be seeing about a seemingly simple property in the class reference, let alone on the Inspector's tooltip.

[TokageItLab]

I rewrote it to leave only the important points, how about one?

[akien-mga]

Thanks!