Add handles to control Curve3D tilt

[xiongyaohua]

This PR add handles to control Curve3D tilt. The implementation of in, out handles are also revamped, as the original ones are too hacky, specifically the mapping between handle ids and control point ids.

tilt_handle_showcase.mov

The behaviour of this PR is similar with PR #68873, but disks are added to indicate the tilt handles trajectories, and an blue radial line is add to indicate the "natural" up vector before tilt.

An internal helper method Curve3D::_get_posture_at_control_point() is added to facilitate tile handle implantation, it could be promoted to an public method if someone found it useful.

When a Path3D is modified by handles, the transform of PathFollow3D is not updated, hence the attached camera view also doesn't change. This issue is fixed by a related PR #80233, which makes tweaking camera easier.

[AThousandShips]

There are review comments that are hidden under the "conversations hidden" that you have missed

Please try to apply them as a batch, to prevent restarting CI several times

[xiongyaohua]

Please try to apply them as a batch, to prevent restarting CI several times

Done. Thanks for the tip! not a regular user of Github.

[akien-mga]

CC @TokageItLab @ajreckof who have been involved in reviewing or improving this plugin recently, IINM.

[TokageItLab]

LGTM, the code style problems were removed and seemed to work fine when I tested.

As for the feedback of usability, I suggest that the TiltHandle should be a different color than the InOut Handle (e.g. yellow line). Also it would be better to be able to change the radius from EditorSetting. Well, we can send the PR for these improvements later.

[AThousandShips]

Code style looks good

[xiongyaohua]

Hi @akien-mga, is it possible to merge this PR earlier than 4.x? I'd like to start working on this proposal and usability improvement mentioned in @TokageItLab's review comment. But they depend on changes in this PR.

[akien-mga]

Thanks!