LibWebView+WebContent: Add an IPC to take a full document screenshot

Author: https://github.com/trflynn89
Commit: 95e591b61b
Pull-request: https://github.com/SerenityOS/serenity/pull/15934

Userland/Libraries/LibWebView/OutOfProcessWebView.h

@@ -86,6 +86,7 @@ public:
 
     Gfx::ShareableBitmap take_screenshot() const;
     Gfx::ShareableBitmap take_element_screenshot(i32 element_id);
+    Gfx::ShareableBitmap take_document_screenshot();
 
     Messages::WebContentServer::WebdriverExecuteScriptResponse webdriver_execute_script(String const& body, Vector<String> const& json_arguments, Optional<u64> const& timeout, bool async);