Cherry pick Swift 5.5 doc changes in TaskGroup.swift

Author: amartini51

stdlib/public/Concurrency/AsyncStream.swift

@@ -279,6 +279,7 @@ public struct AsyncStream<Element> {
     build(Continuation(storage: storage))
   }
 
+   
   /// Constructs an asynchronous stream from a given element-producing
   /// closure, with an optional closure to handle cancellation.
   ///

stdlib/public/Concurrency/TaskCancellation.swift

@@ -15,18 +15,18 @@ import Swift
 
 // ==== Task Cancellation ------------------------------------------------------
 
-/// Execute an operation with cancellation handler which will immediately be
-/// invoked if the current task is cancelled.
+/// Execute an operation with a cancellation handler that's immediately
+/// invoked if the current task is canceled.
 ///
 /// This differs from the operation cooperatively checking for cancellation
 /// and reacting to it in that the cancellation handler is _always_ and
-/// _immediately_ invoked when the task is cancelled. For example, even if the
-/// operation is running code which never checks for cancellation, a cancellation
-/// handler still would run and give us a chance to run some cleanup code.
+/// _immediately_ invoked when the task is canceled. For example, even if the
+/// operation is running code that never checks for cancellation, a cancellation
+/// handler still runs and provides a chance to run some cleanup code.
 ///
-/// Does not check for cancellation, and always executes the passed `operation`.
+/// Doesn't check for cancellation, and always executes the passed `operation`.
 ///
-/// This function returns instantly and will never suspend.
+/// This function returns immediately and never suspends.
 @available(SwiftStdlib 5.1, *)
 public func withTaskCancellationHandler<T>(
   operation: () async throws -> T,
@@ -42,7 +42,10 @@ public func withTaskCancellationHandler<T>(
 
 @available(SwiftStdlib 5.1, *)
 extension Task {
-  /// Returns `true` if the task is cancelled, and should stop executing.
+  /// A Boolean value that indicates whether the task should stop executing.
+  ///
+  /// After the value of this property becomes `true`, it remains `true` indefinitely.
+  /// There is no way to uncancel a task.
   ///
   /// - SeeAlso: `checkCancellation()`
   @_transparent public var isCancelled: Bool {
@@ -52,10 +55,10 @@ extension Task {
 
 @available(SwiftStdlib 5.1, *)
 extension Task where Success == Never, Failure == Never {
-  /// Returns `true` if the task is cancelled, and should stop executing.
+  /// A Boolean value that indicates whether the task should stop executing.
   ///
-  /// If no current `Task` is available, returns `false`, as outside of a task
-  /// context no task cancellation may be observed.
+  /// After the value of this property becomes `true`, it remains `true` indefinitely.
+  /// There is no way to uncancel a task.
   ///
   /// - SeeAlso: `checkCancellation()`
   public static var isCancelled: Bool {
@@ -67,18 +70,9 @@ extension Task where Success == Never, Failure == Never {
 
 @available(SwiftStdlib 5.1, *)
 extension Task where Success == Never, Failure == Never {
-  /// Check if the task is cancelled and throw an `CancellationError` if it was.
-  ///
-  /// It is intentional that no information is passed to the task about why it
-  /// was cancelled. A task may be cancelled for many reasons, and additional
-  /// reasons may accrue / after the initial cancellation (for example, if the
-  /// task fails to immediately exit, it may pass a deadline).
-  ///
-  /// The goal of cancellation is to allow tasks to be cancelled in a
-  /// lightweight way, not to be a secondary method of inter-task communication.
+  /// Throws an error if the task was canceled.
   ///
-  /// ### Suspension
-  /// This function returns instantly and will never suspend.
+  /// The error is always an instance of `Task.CancellationError`.
   ///
   /// - SeeAlso: `isCancelled()`
   public static func checkCancellation() throws {
@@ -88,10 +82,10 @@ extension Task where Success == Never, Failure == Never {
   }
 }
 
-/// The default cancellation thrown when a task is cancelled.
+/// An error that indicates a task was canceled.
 ///
 /// This error is also thrown automatically by `Task.checkCancellation()`,
-/// if the current task has been cancelled.
+/// if the current task has been canceled.
 @available(SwiftStdlib 5.1, *)
 public struct CancellationError: Error {
   // no extra information, cancellation is intended to be light-weight