Fix T82824: Draw sensor size with correct alpha

Previously the option in the camera's //Object Data Properties > Viewport Display
 > Sensor// would not display the sensor in camera view. This seemed to be caused
by the theme color `TH_VIEW_OVERLAY` having zero set for the alpha channel and
alpha blending being active, resulting in no visible output. Hence
`immUniformThemeColorShade(TH_VIEW_OVERLAY, 100);` is replaced with
`immUniformThemeColorShadeAlpha(TH_VIEW_OVERLAY, 100, 255);`.

Reviewed By: mano-wii

Differential Revision: https://developer.blender.org/D11075

source/blender/editors/space_view3d/view3d_draw.c

@@ -778,7 +778,7 @@ static void drawviewborder(Scene *scene, Depsgraph *depsgraph, ARegion *region,
       }
 
       /* draw */
-      immUniformThemeColorShade(TH_VIEW_OVERLAY, 100);
+      immUniformThemeColorShadeAlpha(TH_VIEW_OVERLAY, 100, 255);
 
       /* TODO Was using:
        * UI_draw_roundbox_4fv(false, rect.xmin, rect.ymin, rect.xmax, rect.ymax, 2.0f, color);