Implement extensions GL_OVR_multiview and GL_OVR_multiview2

They are almost identical to the already supported GL_EXT_multiview

Test/300.vert

@@ -184,4 +184,16 @@ void fooDeeparray()
     yp = y;
     xp = y; // ERROR, wrong size
     yp = x; // ERROR, wrong size
+}
+
+void mwErr()
+{
+    gl_ViewID_OVR;   // ERROR, no extension
+}
+
+#extension GL_OVR_multiview : enable
+
+void mwOk()
+{
+    gl_ViewID_OVR;
 }