src: avoid duplicate Before/AtExitCallback structs

Currently, BeforeExitCallback and AtExitCallback are identical apart for
the name of the struct. This commit introduces an ExitCallback struct
with can be used in both cases to avoid the duplication.

PR-URL: #19226
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/env.cc

@@ -218,25 +218,25 @@ void Environment::PrintSyncTrace() const {
 }
 
 void Environment::RunBeforeExitCallbacks() {
-  for (BeforeExitCallback before_exit : before_exit_functions_) {
+  for (ExitCallback before_exit : before_exit_functions_) {
     before_exit.cb_(before_exit.arg_);
   }
   before_exit_functions_.clear();
 }
 
 void Environment::BeforeExit(void (*cb)(void* arg), void* arg) {
-  before_exit_functions_.push_back(BeforeExitCallback{cb, arg});
+  before_exit_functions_.push_back(ExitCallback{cb, arg});
 }
 
 void Environment::RunAtExitCallbacks() {
-  for (AtExitCallback at_exit : at_exit_functions_) {
+  for (ExitCallback at_exit : at_exit_functions_) {
     at_exit.cb_(at_exit.arg_);
   }
   at_exit_functions_.clear();
 }
 
 void Environment::AtExit(void (*cb)(void* arg), void* arg) {
-  at_exit_functions_.push_back(AtExitCallback{cb, arg});
+  at_exit_functions_.push_back(ExitCallback{cb, arg});
 }
 
 void Environment::AddPromiseHook(promise_hook_func fn, void* arg) {

src/env.h

@@ -799,17 +799,13 @@ class Environment {
 
   double* fs_stats_field_array_;
 
-  struct BeforeExitCallback {
+  struct ExitCallback {
     void (*cb_)(void* arg);
     void* arg_;
   };
-  std::list<BeforeExitCallback> before_exit_functions_;
+  std::list<ExitCallback> before_exit_functions_;
 
-  struct AtExitCallback {
-    void (*cb_)(void* arg);
-    void* arg_;
-  };
-  std::list<AtExitCallback> at_exit_functions_;
+  std::list<ExitCallback> at_exit_functions_;
 
   struct PromiseHookCallback {
     promise_hook_func cb_;