refactor: iwyu (#26062)

src/nvim/lua/base64.c

@@ -1,11 +1,16 @@
 #include <assert.h>
 #include <lauxlib.h>
 #include <lua.h>
+#include <stddef.h>
 
 #include "nvim/base64.h"
 #include "nvim/lua/base64.h"
 #include "nvim/memory.h"
 
+#ifdef INCLUDE_GENERATED_DECLARATIONS
+# include "lua/base64.c.generated.h"
+#endif
+
 static int nlua_base64_encode(lua_State *L)
 {
   if (lua_gettop(L) < 1) {

src/nvim/lua/xdiff.c

@@ -13,6 +13,7 @@
 #include "nvim/lua/xdiff.h"
 #include "nvim/macros.h"
 #include "nvim/memory.h"
+#include "nvim/pos.h"
 #include "nvim/vim.h"
 #include "xdiff/xdiff.h"