Fix Animation::subtract_variant for affine transforms

[kleonc]

Transform2D::inverse/Transform3D::inverse which were used in Animation::subtract_variant work only for rotation + translation, don't work for scale, skew, etc.

This resulted in e.g. PropertyTweener incorrectly calculating the delta for affine transforms:

godot/scene/animation/tween.cpp

Line 557 in b8ed596

delta_val = Animation::subtract_variant(final_val, initial_val);

Fixes #79242.

[TokageItLab]

BTW, probably Transform3D skew will be discarded immediately, see also #64418 and #72287.

[YuriSizov]

Thanks!

[YuriSizov]

Cherry-picked for 4.1.2.