Make integer animation tracks be continuous when created

[YeldhamDev]

No description provided.

[TokageItLab]

Also I think BASIS can be added.

[TokageItLab]

And, those cubic interpolation is done by Animation::_cubic_interpolate in animation.cpp, so that may need to be implement it.

[reduz]

I am not sure myself, a lot of things you can animate like states, frames, etc. are also integers. Those work fine now and it would break and be difficult to understand why. On the other hand if something is not continous its easy to understand why and fixing it. It just seems kind of odd to make integer tracks continuous by default. I would be happy if you can explain in which situations do you need this.

[reduz]

At much, we could make it dependant on the hint I think.

[KoBeWi]

While I don't much get the reasoning either (although vaguely remember it being discussed), I tested it and it doesn't seem to break anything, e.g. frame animations are the same as before.

[reduz]

@KoBeWi I think what changes is that the value is sent all the time, and I am not entirely sure if this will work with every property or if every possible property checks that the value is different before doing what needs to be done. If it does check, it may add a hidden performance issue in many cases associated to a state change.

[YeldhamDev]

I would be happy if you can explain in which situations do you need this.

The reason why I made this PR was because I was trying to animate the margins of a Control node, which are integer values. And believe me, it didn't immediately click to me that the reason everything was just directly snapping into place was because the track was set to discrete mode.