Rendering of mjGEOM_LINE respects size[0] (width argument of mjv_makeconnector), denominated in pixels.

- Before this change, line width was hardcoded to 3 pixels and the width argument of mjv_makeConnector was ignored.
- After this change, the width argument is respected and interpreted in units of pixel. The non-standard width unit is ok since lines can only be drawn programmatically.

PiperOrigin-RevId: 516529265
Change-Id: I27bffabba69cde415d2ada67263a887c9240efbf

include/mujoco/mujoco.h

@@ -587,6 +587,7 @@ MJAPI void mjv_initGeom(mjvGeom* geom, int type, const mjtNum size[3],
 
 // Set (type, size, pos, mat) for connector-type geom between given points.
 // Assume that mjv_initGeom was already called to set all other properties.
+// Width of mjGEOM_LINE is denominated in pixels.
 MJAPI void mjv_makeConnector(mjvGeom* geom, int type, mjtNum width,
                              mjtNum a0, mjtNum a1, mjtNum a2,
                              mjtNum b0, mjtNum b1, mjtNum b2);