iwyu: begin/end exports directive for entt.hpp/fwd.hpp (see #777)

src/entt/entt.hpp

@@ -1,3 +1,4 @@
+// IWYU pragma: begin_exports
 #include "config/config.h"
 #include "config/macro.h"
 #include "config/version.h"
@@ -60,3 +61,4 @@
 #include "signal/dispatcher.hpp"
 #include "signal/emitter.hpp"
 #include "signal/sigh.hpp"
+// IWYU pragma: end_exports

src/entt/fwd.hpp

@@ -1,3 +1,4 @@
+// IWYU pragma: begin_exports
 #include "container/fwd.hpp"
 #include "core/fwd.hpp"
 #include "entity/fwd.hpp"
@@ -7,3 +8,4 @@
 #include "process/fwd.hpp"
 #include "resource/fwd.hpp"
 #include "signal/fwd.hpp"
+// IWYU pragma: end_exports