XRBody.size value required to be 25

[mattrossman]

The specification says the size attribute of XRBody must return the number 25.

body-tracking/index.bs

Line 268 in f5727cd

The <dfn attribute for=XRBody>size</dfn> attribute MUST return the number <code>25</code>.

However, in the Quest Browser this returns the number 84, which matches the number of joints listed in the enum.

[Maksims]

I might be a remnant of Hand Tracking that was used as a basis for this spec.