Add IWYU annotations

This allows to use clang-include-cleaner tool without <pipewire/foo.h>
headers being automatically added when <pipewire/pipewire.h> is included
instead.

See https://issues.webrtc.org/issues/422940461

src/pipewire/pipewire.h

@@ -7,6 +7,7 @@
 
 #include <spa/support/plugin.h>
 
+// IWYU pragma: begin_exports
 #include <pipewire/array.h>
 #include <pipewire/client.h>
 #include <pipewire/conf.h>
@@ -36,6 +37,7 @@
 #include <pipewire/type.h>
 #include <pipewire/utils.h>
 #include <pipewire/version.h>
+// IWYU pragma: end_exports
 
 #ifdef __cplusplus
 extern "C" {