GL line width + pixel ratio woes

This is the new home of the GL line width sub-issue in https://github.com/AnalyticalGraphicsInc/cesium/issues/8113

There are two problems with using GL lines with varying resolution scale:
1) Some vendors don't support line widths greater than 1, which results in very thin lines at high pixel densities:

Width 1 at low resolution scale

Width 1 at high resolution scale

2) `RenderState` doesn't have access to `FrameState` which has the `pixelRatio` value. So even if we wanted to multiply the line width with pixel ratio, it would require a refactor.

My thinking is we shouldn't be using GL lines for anything, mainly because of the first problem, and should instead use polylines. Chances are this issue will stay on the back-burner for a while since this is low-impact problem, but glad to hear other's thoughts.

Start with linked issue #8113 and the RenderState/FrameState relationship described here; inspect the existing GL-line and polyline rendering entry points. The issue does not name files, tests, or a settled implementation, so first establish whether GL lines should be removed or made pixel-ratio aware, then validate line appearance across resolution scales.

Written by the indexing model from the issue text.