Fix broken negative scaling when using Jolt Physics

[mihe]

Fixes #103408.
Supersedes #103426.

This PR effectively just brings back some code (derived in part from Jolt's own JPH::Mat44::Decompose) that I had left behind when porting the Jolt integration from the Godot Jolt extension in #99895, due to wanting to keep things as minimal as possible.

What this code is meant to do is take a potentially scaled Basis (or Transform3D) and decompose it into a rotation part and a scale part, which must be done before passing any transform into Jolt, as Jolt takes scale separately from the rest of the transform in its API, and sometimes also takes rotation separately, in the form of a quaternion.

I had mistaken the following code:

Vector3 scale = some_basis.get_scale();
Basis rotation = some_basis.orthonormalized();

... as being a valid substitute for this code:

Basis rotation;
Vector3 scale;
decomposed(some_basis, rotation, scale);

... which it is not, because while Basis::orthonormalize does also use the Gram-Schmidt process to perform the orthonormalization, much like this "new" decompose function, it does not handle reflection (i.e. negative scaling) in any way, meaning we can end up with a Basis that is orthonormal, but is not in fact a valid (right-handed) rotation, which causes problems with things like Basis::get_quaternion, as it assumes a valid (right-handed) rotation.

This "new" decompose function solves this by essentially just flipping all the axes of the Basis when we find ourselves with a negative determinant (i.e. negative scaling) which seems to line up with the convention used by other Basis methods, like Basis::get_scale and Basis::get_rotation_quaternion.

It also serves as a minor optimization, since we can avoid some of the redundant vector normalizations that are shared between Basis::get_scale and Basis::orthonormalize.

[mihe]

I'd love for someone more mathematically inclined than myself to check that I'm not talking too much rubbish here, like perhaps @jrouwe or @rburing (or anyone else who feels up to it).