[iwyu] Reduce includes of <ostream> header

Use <iosfwd> where possible, in particular in public headers
(include/v8-*.h).

R=cbruni@chromium.org

Bug: v8:11879
Change-Id: I9d6095e6385229763d667f5064a794d67952b2b0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3160517Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76956}

include/v8-message.h

@@ -7,7 +7,7 @@
 
 #include <stdio.h>
 
-#include <ostream>
+#include <iosfwd>
 
 #include "v8-local-handle.h"  // NOLINT(build/include_directory)
 #include "v8-maybe.h"         // NOLINT(build/include_directory)

src/codegen/source-position.h

@@ -5,7 +5,7 @@
 #ifndef V8_CODEGEN_SOURCE_POSITION_H_
 #define V8_CODEGEN_SOURCE_POSITION_H_
 
-#include <ostream>
+#include <iosfwd>
 
 #include "src/base/bit-field.h"
 #include "src/common/globals.h"