Concurrency: Revert workarounds for @backDeployed condfails.

All compilers that the standard library's textual interface must support:
- Allow back deployed functions to be declared without `@available`.
- Allow back deployed functions to be `@inlinable`.
- Support `defer` blocks in back deployed functions.

We can therefore revert the workarounds added in
#62946 and
#62928.

Resolves rdar://104085810

Author: tshortli

stdlib/public/BackDeployConcurrency/TaskCancellation.swift

@@ -38,22 +38,17 @@ import Swift
 /// the operation gets to run.
 @_unsafeInheritExecutor // the operation runs on the same executor as we start out with
 @available(SwiftStdlib 5.1, *)
-@_backDeploy(before: SwiftStdlib 5.8)
+@backDeployed(before: SwiftStdlib 5.8)
 public func withTaskCancellationHandler<T>(
   operation: () async throws -> T,
   onCancel handler: @Sendable () -> Void
 ) async rethrows -> T {
   // unconditionally add the cancellation record to the task.
   // if the task was already cancelled, it will be executed right away.
   let record = _taskAddCancellationHandler(handler: handler)
-  do {
-    let result = try await operation()
-    _taskRemoveCancellationHandler(record: record)
-    return result
-  } catch {
-    _taskRemoveCancellationHandler(record: record)
-    throw error
-  }
+  defer { _taskRemoveCancellationHandler(record: record) }
+
+  return try await operation()
 }
 
 @available(SwiftStdlib 5.1, *)

stdlib/public/BackDeployConcurrency/TaskLocal.swift

@@ -135,10 +135,10 @@ public final class TaskLocal<Value: Sendable>: Sendable, CustomStringConvertible
   ///
   /// If the value is a reference type, it will be retained for the duration of
   /// the operation closure.
+  @inlinable
   @discardableResult
   @_unsafeInheritExecutor
-  @available(SwiftStdlib 5.1, *) // back deploy requires we declare the availability explicitly on this method
-  @_backDeploy(before: SwiftStdlib 5.8)
+  @backDeployed(before: SwiftStdlib 5.8)
   public func withValue<R>(_ valueDuringOperation: Value, operation: () async throws -> R,
                            file: String = #file, line: UInt = #line) async rethrows -> R {
     return try await withValueImpl(valueDuringOperation, operation: operation, file: file, line: line)
@@ -165,8 +165,7 @@ public final class TaskLocal<Value: Sendable>: Sendable, CustomStringConvertible
   @inlinable
   @discardableResult
   @_unsafeInheritExecutor
-  @available(SwiftStdlib 5.1, *) // back deploy requires we declare the availability explicitly on this method
-  @_backDeploy(before: SwiftStdlib 5.9)
+  @backDeployed(before: SwiftStdlib 5.9)
   internal func withValueImpl<R>(_ valueDuringOperation: __owned Value, operation: () async throws -> R,
                                  file: String = #fileID, line: UInt = #line) async rethrows -> R {
     // check if we're not trying to bind a value from an illegal context; this may crash

stdlib/public/Concurrency/TaskCancellation.swift

@@ -38,22 +38,17 @@ import Swift
 /// the operation gets to run.
 @_unsafeInheritExecutor // the operation runs on the same executor as we start out with
 @available(SwiftStdlib 5.1, *)
-@_backDeploy(before: SwiftStdlib 5.8)
+@backDeployed(before: SwiftStdlib 5.8)
 public func withTaskCancellationHandler<T>(
   operation: () async throws -> T,
   onCancel handler: @Sendable () -> Void
 ) async rethrows -> T {
   // unconditionally add the cancellation record to the task.
   // if the task was already cancelled, it will be executed right away.
   let record = _taskAddCancellationHandler(handler: handler)
-  do {
-    let result = try await operation()
-    _taskRemoveCancellationHandler(record: record)
-    return result
-  } catch {
-    _taskRemoveCancellationHandler(record: record)
-    throw error
-  }
+  defer { _taskRemoveCancellationHandler(record: record) }
+
+  return try await operation()
 }
 
 @available(SwiftStdlib 5.1, *)

stdlib/public/Concurrency/TaskLocal.swift

@@ -135,10 +135,10 @@ public final class TaskLocal<Value: Sendable>: Sendable, CustomStringConvertible
   ///
   /// If the value is a reference type, it will be retained for the duration of
   /// the operation closure.
+  @inlinable
   @discardableResult
   @_unsafeInheritExecutor
-  @available(SwiftStdlib 5.1, *) // back deploy requires we declare the availability explicitly on this method
-  @_backDeploy(before: SwiftStdlib 5.8)
+  @backDeployed(before: SwiftStdlib 5.8)
   public func withValue<R>(_ valueDuringOperation: Value, operation: () async throws -> R,
                            file: String = #fileID, line: UInt = #line) async rethrows -> R {
     return try await withValueImpl(valueDuringOperation, operation: operation, file: file, line: line)
@@ -165,8 +165,7 @@ public final class TaskLocal<Value: Sendable>: Sendable, CustomStringConvertible
   @inlinable
   @discardableResult
   @_unsafeInheritExecutor
-  @available(SwiftStdlib 5.1, *) // back deploy requires we declare the availability explicitly on this method
-  @_backDeploy(before: SwiftStdlib 5.9)
+  @backDeployed(before: SwiftStdlib 5.9)
   internal func withValueImpl<R>(_ valueDuringOperation: __owned Value, operation: () async throws -> R,
                                  file: String = #fileID, line: UInt = #line) async rethrows -> R {
     // check if we're not trying to bind a value from an illegal context; this may crash