Discontinue exp map in blending

[TokageItLab]

Fixed #60306. Discontinue the use of exp map in blending.

The exp map can easily perform multiple quaternion blends. However, it really comes into its own when you need to compute two or more quaternions at the same time, such as when diverting the cubic interpolate formula in an issue like #57951, which is what we are trying to solve now.

In the blending process, quaternions are always complemented one by one by the iterator, so there is not much point in using exp map. The calculation cost is much lower, but the error is larger when there are large rotations, as in #60306. See #58043 and https://swkagami.hatenablog.com/entry/lie_03algebra for a description of the error of the exp map.

Actually, in fact I replaced slerp and confirmed before that it does more than 3 blends correctly.

Here is the video after the fix:

2022-04-17.4.13.41-1.mov

In the opening of the video above you can see that changing the connection order for blending more than 3 Nodes is not a problem, prior to 4.0.alpha4 these results were different and the calculations were not done correctly in the first place.

Earlier, reduz said there was a problem with slerp from an empty quaternion as in #34134 (comment), it was that a 180 degree rotation from the init quaternion from always could not be done. In fact, we can use any base quaternion by adding init_rot to the calculation, so we don't have to worry about that problem.

[fire]

The test cases look ok, but I'm not able to review as much in depth.

[akien-mga]

Thanks!