[api] Add missing V8_EXPORT_PRIVATE annotation

This caused compile errors since https://crrev.com/c/1934407:
ld.lld: error: undefined symbol: v8::debug::AccessorPair::CheckCast(v8::Value*)
>>> referenced by debug-interface.h:578 (../../src/debug/debug-interface.h:578)
>>>               obj/test/cctest/cctest_sources/test-debug.o:(TestGetPrivateMethodsAndAccessors())

R=verwaest@chromium.org
CC=joyee@igalia.com

Change-Id: I4a727ddd2673c75ec16368459114cfcafdd18912
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1955595
Auto-Submit: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Joyee Cheung <joyee@igalia.com>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65381}

src/debug/debug-interface.h

@@ -527,13 +527,13 @@ class WeakMap : public v8::Object {
  * In the case of private accessors, getters and setters are either null or
  * Functions.
  */
-class AccessorPair : public v8::Value {
+class V8_EXPORT_PRIVATE AccessorPair : public v8::Value {
  public:
-  V8_EXPORT_PRIVATE v8::Local<v8::Value> getter();
-  V8_EXPORT_PRIVATE v8::Local<v8::Value> setter();
+  v8::Local<v8::Value> getter();
+  v8::Local<v8::Value> setter();
 
-  V8_EXPORT_PRIVATE static bool IsAccessorPair(v8::Local<v8::Value> obj);
-  V8_INLINE V8_EXPORT_PRIVATE static AccessorPair* Cast(v8::Value* obj);
+  static bool IsAccessorPair(v8::Local<v8::Value> obj);
+  V8_INLINE static AccessorPair* Cast(v8::Value* obj);
 
  private:
   AccessorPair();