Bug 1742168, increase maxStateObjectSize to 16MB and make the pref a StaticPref, r=peterv

Keeping the pref as signed, since the existing code explicitly handles that case, so someone may have -1 as the pref value.

Differential Revision: https://phabricator.services.mozilla.com/D132020

docshell/base/nsDocShell.cpp

@@ -11114,9 +11114,7 @@ nsDocShell::AddState(JS::Handle<JS::Value> aData, const nsAString& aTitle,
   }
 
   // Check that the state object isn't too long.
-  // Default max length: 2097152 (0x200000) bytes.
-  int32_t maxStateObjSize =
-      Preferences::GetInt("browser.history.maxStateObjectSize", 2097152);
+  int32_t maxStateObjSize = StaticPrefs::browser_history_maxStateObjectSize();
   if (maxStateObjSize < 0) {
     maxStateObjSize = 0;
   }