GLTF export: Remove snapping and fix validation

[lyuma]

Fixes almost all validation warnings and errors on gtlf exports.

• Round min/max correctly in accessors
• Include correct target in vertex and indices bufferViews
• Avoid use of Math::snapped
• Normalize vertex weights.

I do still occasionally encounter a vertex which appears to round differently in min/max calculation and I don't know why:

ACCESSOR_MIN_MISMATCH	Declared minimum value for this component (-8.310235699582336e-8) does not match actual minimum (-8.310236410125071e-8).	/accessors/29/min/2
ACCESSOR_ELEMENT_OUT_OF_MIN_BOUND	Accessor contains 6 element(s) less than declared minimum value -8.310235699582336e-8.	/accessors/29/min/2

It is off by roughly 1.5e-14 which is really small but my guess is it's somehow the adjacent float value from a e-8

[fire]

Needs to pass cicd but looks good. We discussed the problem on Discord.

[akien-mga]

Thanks!