LibWeb/WebGL: Move extensions into their own folder

Author: https://github.com/Lubrsi
Commit: de77a5e3ea
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

@@ -841,8 +841,6 @@ struct OscillatorOptions;
 }
 
 namespace Web::WebGL {
-class ANGLEInstancedArrays;
-class OESVertexArrayObject;
 class OpenGLContext;
 class WebGL2RenderingContext;
 class WebGLActiveInfo;
@@ -860,6 +858,11 @@ class WebGLSync;
 class WebGLTexture;
 class WebGLUniformLocation;
 class WebGLVertexArrayObject;
+}
+
+namespace Web::WebGL::Extensions {
+class ANGLEInstancedArrays;
+class OESVertexArrayObject;
 class WebGLVertexArrayObjectOES;
 }