LibWeb/WebGL: Implement WEBGL_draw_buffers extension

Author: https://github.com/Lubrsi
Commit: 55f7cb4f10
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3239
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/kalenikaliaksandr

Libraries/LibWeb/Forward.h

@@ -863,6 +863,7 @@ class WebGLVertexArrayObject;
 namespace Web::WebGL::Extensions {
 class ANGLEInstancedArrays;
 class OESVertexArrayObject;
+class WebGLDrawBuffers;
 class WebGLVertexArrayObjectOES;
 }