Tileset Highlighting Distortion (M1 hardware on iOS 12)

Highlights on 3D Tiles appear distorted when running CesiumJS on a MacBook with an M1 chip. This issue occurs when the M1 MacBook is running iOS 12 and does ***not*** occur when it is running iOS 11.
We ran a [WebGL report](https://webglreport.com/) on Google Chrome using two devices:
- M1 MacBook running iOS 12 (3D Tiles highlights issue is visible)
- Intel MacBook running iOS 11 (no issue with 3D Tiles highlights)

The differences between the two WebGL reports are:
- WEBGL_video_texture is on the M1 Pro and not the Intel
- Max Varying Vectors
- Max Vertex Output Components
- Different values on Aliased Point Size Range
- Different values on Max Samples in Framebuffer

These differences in supported extensions do not seem relevant to the tileset highlighting issue. Thus, it is likely a "deeper" issue with our specification.

Sandcastle example:
https://sandcastle.cesium.com/?src=Classification.html
Browser:
Chrome
Operating System:
M1 MacBook Pro (OS12)

cc @lilleyse @ebogo1

Start with the Classification.html Sandcastle example in Chrome on an M1 MacBook running OS 12 and reproduce the distorted 3D Tiles highlights. Compare the result with the reported OS 11 behavior and the linked WebGL reports, then determine the rendering cause and verify that highlighting is no longer distorted on the affected configuration.

Written by the indexing model from the issue text.