Thank you so much for the pull request @nmschulte-aviture! I noticed this is your first pull request and I wanted to say welcome to the Cesium community!

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We have a signed CLA from Aviture for username nmschulte. Did you have your GitHub username changed?

Was there an open issue for this bug? If so, can you link it? If not, can you provide a Sandcastle example of the bug this PR fixes, to make this easier to review?

We have a signed CLA from Aviture for username nmschulte. Did you have your GitHub username changed?

I operate both usernames, @nmschulte and @nmschulte-aviture. If I need to amend the CLA somehow that is fine; if I simply need to voice approval as @nmschulte I can do that as well.

Was there an open issue for this bug? If so, can you link it? If not, can you provide a Sandcastle example of the bug this PR fixes, to make this easier to review?

I do not know of any open issues addressing these concerns. I can create a test/example case for the rtc Array length logic bug but it'd be contrived. As well, I can create a test/example case for the resource freeing, but again they'll be contrived.

This command should show that the _pickSP code in Primitive isn't necessary:
git show -s HEAD && git grep _pickSP

Sandcastle example showing issue with depth-fail's shader program not cleaning up:
https://cesiumjs.org/Cesium/Apps/Sandcastle/index.html#c=vVZtb9s2EP4rRD40NKLSkiVZUuIEM5I0CNY6QWOsGOpiYCTaJkqLAkk78wb/951eIytOCgxF88ERj/c8d/foeNSGKrTh7IkpdI5S9oQumebrFfmjsOHjuFheytRQnjJ1bKF/ZymCP8OUAtO9khueMHVaA2PFqGFfpBLJtHTBvVm6653N0g3E0jFLGYQqY5JiCVuztHgiCyEfGUlYZpZTps14AXhtKiKAGbUu3XOuTIqt4OmzQbB0YZbg5ti23Vi1ocp8lDm8yvETNUti5GeacJpqHA5J5LtB5NZJsjT5gX8YDb0o6D1HpuZV90FAojAc+C33SrwHusoEu5eaGy5TDQxfv4HPXCqEczcOFvsM/o2q0s7QyQnv1a+gCPwiT8FUhssKrKZ2C0j6CFcCvUdOL0+mJsmqDPZb4BKgcqFotuQxFjkHVFnDDldAsrVe4pou993lJVeET0uW4upZF8DqxX6S2lwx6DDBElx1Rqe/rFci9iw0X6dx/oxLTr2nj5zPNTNFSxC7yv2QvhWWHNI5/6v2v/JvZMn4YmnQyXlFXrEWleYPdVvuq3mv+ApS3jDcYl0wuWJGbW+hyWkKZ+20Dbnp7LaRbfQe6L6KXoO7oDLDSr3m1F4LwTMteUK+3DyEHolb734Mum+nMm8HcKZpsW7Etl7SUxVPtxlryMflmkzuJtcH3J94YpanyO9s7brUPDlFx7W4x51Naozij2uTS3ig4lgKqfZ0uswtXYXHNQuZK7kqXHDbn9x9Hk9urg8VXcysD9DClz8p1P3t5PduoF1rvacPzTJGVc57sBkKxnHj0+0JA1Yt1jCBzSmaU6HZa3GaKse/IOCuHJjF8Stuh6w+Q5rQJMF1Lzy7FbOVqkVx4jujrOhdF7u2HQQ28e0wGLhh5Iaehfyh60XOgDiu40aeH/oWGkRB6PgDMgiHvu/5jjOsJ18zUQ7zA5VHosCzo3AYhP5wYKH3cLUQ13OiIArt0Ak8B/i9KIJbxw7DoR0MXWc4aAZyOf9iumKKEiHl97HBZVFWFfwt12kuLUy4FX6+FBT/2yO3V9eT6e30zxpc/rZHc60ngSs82cLkXXF4Mc18RXh/IjIz5Ssm1wa/4lEevFRLwSC5BS4OL/DDMUYnzZgkXF/BVa/kFoZ/cy29ii8gf+msQwKW/0l0Vbf0S8Zm623qF82p2ErCoG/35w9T+Ymi4LYJvXv3lkq/SKYddDx8k9Wm4mTDz5F1NNJmK9hFaf+NrzKpDForgQnpGwZ3DHxN6v7jOv7ODIm1zpGjfg0aJXwDF8P57KjzoTo7QrGgWsPOfC3EA/+HzY4uRn3w34MJCV9p6eJuw5Sg29xl6Vx8LI2EkFEfli9RRkrxSFWL8T8

The above example also seems to show a problem with ShaderProgram's destroy; it also has a finalDestroy method which seems like what I'd expect destroy to be, so I'm sure I'm missing something here.

Sandcastle example showing issue with relative-to-center coordinate rendering check:
https://cesiumjs.org/Cesium/Apps/Sandcastle/index.html#c=ZY5NS8QwEIb/SsiphSXB6262CD2IICh4NB6y6bgbzEeZTCp12f9utBRWndu87/MMMxlkI7rgyE3A9izCB+shuxLE0xo3Zx1ZnSOkAITzfcxkooW8ZS9X/N2fujmvwpYRFri0r5vlEJLtIRLgUtT00u74hqtMs4dugW5dGBMSK+gbISRBGL0hyPJQ7DuQsDm3Ox2VXCU1uIm5Ya+5/XmoT5GMi4CaM+tNzrV5K94/u0/QvFOy8r80n8zg4vFxAvRm/kZON93DEgohlKzrf4tS8geDVxe/AA

Thanks @nmschulte-aviture! This looks good. I'll merge as soon as CI passes

Thanks for the awesome work @nmschulte-aviture! Your contribution is about to launch to millions of users with the next release. 🚀

Do you mind if we tweet about it? CC @OmarShehata @slchow.