Reworked geometric algebra. Accesses Basis via get_column.

[The-Cyber-Captain]

… to 'correct' root and shoulder-tracking bugs respectively.

Root tracker does now point 'forward'. IE +z aligns with hips & user's real-world 'forward' (whilst remaining along, and on, the XRorigin / Global XZ plane). Shoulder trackers also properly pulled back (the previously indicated 7cm) towards upper chest, more aligned with T-pose modelling.

Having now delved a bit deeper into GDE wrappers, variants exposure, etc, I'm going to speculate that basis' unit vectors are, indeed, intended to be accessed via get_column out here - as we're firmly in C++ land still - and that's what initially tripped @m4gr3d up way back when? I've done a quick search of the files in GodotVR repo and couldn't find any others which access 'basis[]' beyond this file which would need addressing.

Primarily fixes #205, & fixes #218, though leaves open discussion still re:

• the approach of omitting / dropping XR_BODY_JOINT_<#####>SCAPULA_FB data, then correction of XR_BODY_JOINT<#####>_SHOULDER_FB, and techniques employed therein.
• modifying root at all!

[The-Cyber-Captain]

Tested as working here for 4.3-stable and 4.4-dev1 on both Quest2 and Quest3.

Neater code - from a slightly more knowledgeable position and tidied up dev env on my side - than the now discarded #209. Should pass clang* etc too this time around.

*Puts the magic into autoMAGIC that does, as far as my wee storyteller [Film / XR] brain is concerned.