make exec::task's environment public

Author: ericniebler

include/exec/task.hpp

@@ -303,6 +303,7 @@ namespace exec {
     template <class _Ty, class _Context = default_task_context<_Ty>>
     class [[nodiscard]] basic_task {
       struct __promise;
+      using __promise_context_t = typename _Context::template promise_context_t<__promise>;
      public:
       using __t = basic_task;
       using __id = basic_task;
@@ -317,6 +318,10 @@ namespace exec {
           __coro_.destroy();
       }
 
+      auto get_env() const noexcept -> const __promise_context_t& {
+        return __coro_.promise().get_env();
+      }
+
      private:
       struct __final_awaitable {
         static constexpr auto await_ready() noexcept -> bool {
@@ -332,8 +337,6 @@ namespace exec {
         }
       };
 
-      using __promise_context_t = typename _Context::template promise_context_t<__promise>;
-
       struct __promise
         : __promise_base<_Ty>
         , with_awaitable_senders<__promise> {