Adds support for the following new WebGL2 GetParameter values:

- `PACK_ROW_LENGTH`
- `PACK_SKIP_PIXELS`
- `PACK_SKIP_ROWS`
- `RASTERIZER_DISCARD`
- `UNPACK_IMAGE_HEIGHT`
- `UNPACK_ROW_LENGTH`
- `UNPACK_SKIP_IMAGES`
- `UNPACK_SKIP_PIXELS`
- `UNPACK_SKIP_ROWS`

See: https://www.khronos.org/registry/webgl/specs/latest/2.0/#3.7.2