Support POLYGON_MODE_LINE and POLYGON_MODE_POINT for GL

[LucaCiucci]

Is your feature request related to a problem? Please describe.
I'm trying to use wgpu in a tauri application (compiling for wasm32), I need to draw some lines and points so I tried to request Features::POLYGON_MODE_LINE and Features::POLYGON_MODE_POINT using a GL backend, but the Adapter::request_device function returns an error if these features are requested.

Describe the solution you'd like
Support these two polygon modes for the GL backend.

Describe alternatives you've considered
Use PrimitiveTopology::LineList or PrimitiveTopology::PointList, but POLYGON_MODE_* could simplify the usage in some cases, for example when switching the representation of a mesh to wireframe or points.

Additional context
None.

[cwfitzgerald]

glPolygonMode seems to be completely unsupported on GLES outside of GL_NV_polygon_mode which has basically zero support, so this is unfortunately not really feasible to support