minor tidy up of v8/include/v8.h

Moves a forward declaration of v8::CFunction to the appropriate
position.

Change-Id: I9ea8c7697a0abd39a0c8fdc536aae0417e04cafe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2359091
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69424}

include/v8.h

@@ -45,6 +45,7 @@ class BigInt;
 class BigIntObject;
 class Boolean;
 class BooleanObject;
+class CFunction;
 class Context;
 class Data;
 class Date;
@@ -6356,7 +6357,6 @@ typedef bool (*AccessCheckCallback)(Local<Context> accessing_context,
                                     Local<Object> accessed_object,
                                     Local<Value> data);
 
-class CFunction;
 /**
  * A FunctionTemplate is used to create functions at runtime. There
  * can only be one function created from a FunctionTemplate in a