Put WL_DEPRECATED in front of the function declarations
This fixes the following clang error when using C23:
../src/wayland-server-core.h:680:41: error: 'deprecated' attribute cannot be applied to types
680 | int32_t stride, uint32_t format) WL_DEPRECATED;
| ^
../src/wayland-util.h:52:25: note: expanded from macro 'WL_DEPRECATED'
52 | #define WL_DEPRECATED [[deprecated]]
| ^