[clang-tidy] Make deleted member functions public

Making them private was a way to hide the functions, we can
explicitly delete them, which give a better compilation error message as
well.

Also see: https://stackoverflow.com/q/55205874

Bug: v8:10488
Change-Id: I24f70dc1f6fb227185b6f8ecb30a81e218dd2a50
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2223232Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68186}

src/libplatform/default-foreground-task-runner.h

@@ -25,11 +25,10 @@ class V8_PLATFORM_EXPORT DefaultForegroundTaskRunner
     explicit RunTaskScope(
         std::shared_ptr<DefaultForegroundTaskRunner> task_runner);
     ~RunTaskScope();
-
-   private:
     RunTaskScope(const RunTaskScope&) = delete;
     RunTaskScope& operator=(const RunTaskScope&) = delete;
 
+   private:
     std::shared_ptr<DefaultForegroundTaskRunner> task_runner_;
   };