LibGL: Implement glDepthFunc

Author: https://github.com/sunverwerth
Commit: 5b9c87a8b5
Pull-request: https://github.com/SerenityOS/serenity/pull/9451
Reviewed-by: https://github.com/Quaker762 ✅
Reviewed-by: https://github.com/alimpfard

Userland/Libraries/LibGL/SoftwareRasterizer.h

@@ -31,6 +31,7 @@ struct RasterizerOptions {
     u32 color_mask { 0xffffffff };
     float depth_min { 0 };
     float depth_max { 1 };
+    GLenum depth_func { GL_LESS };
 };
 
 class SoftwareRasterizer final {