USDZExporter: Improve UsdTransform2d

[hybridherbst]

This PR fixes UsdTransform2d rotation for usdview and other USD-spec-compliant viewers that support the UsdTransform2d schema.
Notably, QuickLook does things differently. There is currently a const in the code to switch between QuickLook behaviour (which is not 100% correct yet, but comes close) and proper behaviour. Unfortunately there doesn't seem to be a way to make both happy until Apple fixes their bugs.

I believe we want to default to the QuickLook behaviour (and hopefully get that fixed) since e.g. model-viewer's main target is conversion to that.

Here is a better test file - the glTF sample model is not sufficiently accurate to show the QuickLook errors:
BetterTextureTransformTests.zip

Viewer	exportForQuickLook=true	exportForQuickLook=false
three.js (ground truth)
usdview
QuickLook

This contribution is funded by Needle

[mrdoob]

Very nice!

[mrdoob]

I believe we want to default to the QuickLook behaviour (and hopefully get that fixed) since e.g. model-viewer's main target is conversion to that.

I feel like exportForQuickLook=false should be the default behaviour.
And add a new option in parse() so <model-viewer> can enable it for now.

[hybridherbst]

cc @elalish

[hybridherbst]

new option in parse()
Like this?

[mrdoob]

Yeah!

[elalish]

Looks great, thanks!