Vector tiles don't always work in 2D and CV

Vector tiles are not well supported in 2D and CV. They use an ECEF based RTC value that doesn't adjust when switching to 2D or CV. And unlike regular polylines we don't store 2D position for vector tile polylines.

One example where the tileset disappears when switching to Columbus View: [Sandcastle](https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/#c=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).

Start by reproducing the linked Sandcastle example and inspect vector-tile rendering when switching between 3D, 2D, and Columbus View. Trace how the ECEF RTC value and polyline positions are handled in each mode. Done means vector-tile polylines remain visible and correctly positioned after those view changes.

Written by the indexing model from the issue text.