Hopefully this is an improvement and not just a rewrite. Some ideas were:
1. Keep poses in WMR space as much as possible.
2. Add an explicit function that precomputes a handful of transforms that allow
converting between WMR and OpenXR coordinates.
3. Make naming of variables in line with a relatively common T_A_B notation.
4. I wasn't able to figure out why `wmr_config_compute_pose` worked before,
in any case, hopefully the new notation convention helps understanding
why P_oxr_{acc,gyr} work.