Review comment: Add IWYU for the vast dependency.

Author: hzeller

xls/public/BUILD

@@ -264,6 +264,7 @@ cc_library(
         ":c_api_format_preference",
         ":c_api_impl_helpers",
         ":c_api_ir_builder",
+        ":c_api_vast",
         ":runtime_build_actions",
         "//xls/common:init_xls",
         "//xls/common/file:filesystem",

xls/public/c_api.h

@@ -21,6 +21,7 @@
 #include "xls/public/c_api_dslx.h"
 #include "xls/public/c_api_format_preference.h"
 #include "xls/public/c_api_ir_builder.h"
+#include "xls/public/c_api_vast.h"  // IWYU pragma: export
 
 // C API that exposes the functionality in various public headers in a way that
 // C-based FFI facilities can easily wrap.