Fix camera zooming in 3D orthographic mode when pixelRatio is not 1

[andrewda]

Description

Zooming in 3D orthographic view is broken at high camera heights when pixel ratio is not 1. See the attached video:

CleanShot.2025-02-19.at.11.52.56.mp4

This PR fixes that behavior by considering the pixel ratio in the orthographic frustum width calculation:

CleanShot.2025-02-19.at.11.53.32.mp4

Issue number and link

#12486

Testing plan

https://sandcastle.cesium.com/#c=bZBBa8MwDIX/ismpheKw65qGbYXtMih0YydfXEdNzGwpSHZCN/bfl7SX0VW3J71PesgRSlKDhxFYbRTCqLYgPkf9ce4tTOHOekuYrEdgU6zUt0GlssAT0yjAe3AUI2ADzR6EQk6e8F4dbRBYGfxZrg0avBzR4gBBt4EOoKWj8YUpY/OYIknfAcOU4gyurwhnI7DVMvrkunfaceqoZdt33j1zlpTjYrkuVkUl6RSgnhPO9eBjT5xU5rDQukwQ+2ATSHnI7hOSdiJzvNlalX/RqvGD8s3mxgOUC1ZkmhxzCG/+C0xRV+Xk/4cGso3HdjcAB3uabd1d/Xppaq2rcpK3yUQUDpavNv8C

const viewer = new Cesium.Viewer("cesiumContainer", {
  useBrowserRecommendedResolution: false,
});

viewer.scene.globe.showGroundAtmosphere = false;
viewer.scene.camera.switchToOrthographicFrustum();

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @andrewda!

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