Update gltf-pipeline

[lilleyse]

Fixes #5856

This makes cesium and gltf-pipeline fully in-sync.

Notes on some of these changes are here: CesiumGS/gltf-pipeline#324

[cesium-concierge]

@lilleyse, thanks for the pull request! Maintainers, we have a signed CLA from @lilleyse, so you can review this at any time.

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[mramato]

In the future, can we include the git hash of the pipeline version in the commit message so that we know exactly where it came from?

[mramato]

Everything appears to be working fine. Thanks @lilleyse!