Full Body IK

[HexaField]

Summary

Full Body IK Implementation

• pre-cache height & other necessary measurements based on bone structure in rig component upon avatar load
  • h: head to foot, a: head to hips, b: hips to knee, c: knee to feet
• write a simple solver for the head/hip/knee/feet offsets
  • calculate internal angle (A) based on cosine rule
  • calculate opposite angle base on sine rule against right angle
  • get z, y from resulant triangle
• do two bone solve from from hips to feet using knee as swing/twist
• apply angle to hips to orient torso
• rotate feet to make them flat to the ground
• ensure translating & rotating the avatar does not break (only been using the developer test suite examples which have the test avatar at the original)
• ensure existing arm and head look IK work as intended (may need to update matrices)
• test with headsets & ensure networking works correctly

Other Fixes

• debug helper & gizmo state fixes used in testing
• improve spectate mode api

References

closes #7486

Checklist

• If this PR is still a WIP, convert to a draft
• ensure all checks pass
• When this PR is ready, mark it as "Ready for review"
• Changes have been manually QA'd
• Changes reviewed by at least 2 approved reviewer

QA Steps

List any additional steps required to QA the changes of this PR, as well as any supplemental images or videos.

[mrhegemon]

Hip solver is so cool.