Fix the explanation of flow emit constraints

[seyoungcho2]

In this part, it says that it checks whether it's the same coroutine, but in the actual implementation, it checks whether it's the same CoroutineContext rather than the same coroutine.

Specifically, in the case of the withContext example, although it internally creates a DispatchedCoroutine object, this is only for context switching, and it still maintains the same coroutine.

val myFlow = flow {
     // GlobalScope.launch { // is prohibited
     // launch(Dispatchers.IO) { // is prohibited
     // withContext(CoroutineName("myFlow")) { // is prohibited
     emit(1) // OK
     coroutineScope {
         emit(2) // OK -- still the same coroutine
     }
 }

Therefore, it might be less confusing to describe this as checking for the same coroutine context rather than the same coroutine.