Rename odd PathFollow2D/3D methods

[TokageItLab]

These are inconsistent with other parts.

[TokageItLab]

Renamed to

<member name="cubic_interpolation" type="bool" setter="set_use_cubic_interpolation" getter="is_using_cubic_interpolation" default="true">

[aaronfranke]

I'm not an active user of PathFollow* but this rename makes sense to me. We could merge for 4.0.

[akien-mga]

If we want this merged for 4.0, then it needs to handle the old property name with _set and _get virtual methods so that it doesn't break users scenes and scripts (unless they use the methods, which we don't bother handling for now).

[TokageItLab]

@akien-mga added (I guess it was only the setter that broke the scene)

[TokageItLab]

Also added a getter for now.

[akien-mga]

So actually I feel the better naming (and somewhat consistent with many other books) would be:

cubic_interpolation, set_cubic_interpolation / is_cubic_interpolation_enabled

It's not perfect as it doesn't make clear that false means linear interpolation instead of no interpolation, but it's less awkward that "use" IMO.

[TokageItLab]

@akien-mga rrrenamed!

[akien-mga]

I'm still not convinced by swapping the order of the words only for the getter (is_interpolation_cubic). What I had suggested was set_cubic_interpolation/is_cubic_interpolation_enabled.

All in all, I find this change quite nitpicky and while I agree that cubic_interpolation is a better property name than cubic_interp (we try to avoid abbreviations), I think on the day of the RC1 release the ship has sailed for this kind of consistency renaming.

[TokageItLab]

@akien-mga Sorry, I was already tired and my mind didn't seem to be working😵‍💫 Here is my last rename.

[TokageItLab]

@akien-mga decided this was too late for 4.0RC, so it is merged into #72842 and this will be done in 4.1.