Orthographic frustum glitches when the camera's direction is parallel to the ground

Hi all,

I am experiencing a frustum bug when I use the orthographic frustum in the 3D Cesium mode. It happens when the camera’s direction is parallel or almost parallel to the ground. Sometimes the camera glitches when the angle between the camera’s direction and the ground is higher. Also, I noticed that scrolling doesn’t work well in the frustum mode. Even though I scroll the mouse only backward, it can be seen the sometimes camera moves forwards, and then back, and then forward again.

I have provided a sandcastle example, but to feel better the bug is useful to go around with mouse while having a low angle between camera and ground.

**Sandcastle example:**
https://sandcastle.cesium.com/#c=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

**Browser:**
Firefox
Chromium,

**Operating System:**
Linux Mint 20

Start with the linked Sandcastle example and reproduce the orthographic-frustum behavior in Cesium's 3D mode while moving the mouse and scrolling at a low camera angle. Trace the camera/frustum entry point reached by that example; done means parallel or near-parallel views no longer glitch and backward-only scrolling does not reverse direction.

Written by the indexing model from the issue text.