[Concurrent] Restored old symbol for obsoleted Task.startSynchronously

#80821 added `@isolated(any)`
which is an ABI breaking change but since we are not planning to keep
this API around, let's use `@_silgen_name` to bring the old name back
for now.

Resolves: rdar://152178221

Author: xedin

stdlib/public/Concurrency/Task+immediate.swift.gyb

@@ -32,8 +32,16 @@ import Swift
 @available(SwiftStdlib 6.2, *)
 extension Task where Failure == ${FAILURE_TYPE} {
 
+  // FIXME: This method is left in place to give adopters time to switch to `immediate` but it's going
+  // to be removed soon, since this spelling was rejected as part of SE-0472 proposal.
   @available(SwiftStdlib 6.2, *)
   @available(*, deprecated, renamed: "immediate")
+  // Used to preserve the symbols as originally declared without `@isolated(any)` attribute on `operation:`.
+  % if FAILURE_TYPE == "Error":
+  @_silgen_name("$sScTss5Error_pRs_rlE18startSynchronously4name8priority_ScTyxsAA_pGSSSg_ScPSgxyYaKcntFZ")
+  % elif FAILURE_TYPE == "Never":
+  @_silgen_name("$sScTss5NeverORs_rlE18startSynchronously4name8priority_ScTyxABGSSSg_ScPSgxyYaKcntFZ")
+  % end
   @discardableResult
   public static func startSynchronously(
     name: String? = nil,

test/abi/macOS/arm64/concurrency.swift

@@ -391,8 +391,8 @@ Added: _swift_task_getCurrentTaskName
 
 // startSynchronously, immediate, addImmediateTask{UnlessCancelled}
 Added: _swift_task_immediate
-Added: _$sScTss5Error_pRs_rlE18startSynchronously4name8priority_ScTyxsAA_pGSSSg_ScPSgxyYaKYAcntFZ
-Added: _$sScTss5NeverORs_rlE18startSynchronously4name8priority_ScTyxABGSSSg_ScPSgxyYaKYAcntFZ
+Added: _$sScTss5Error_pRs_rlE18startSynchronously4name8priority_ScTyxsAA_pGSSSg_ScPSgxyYaKcntFZ
+Added: _$sScTss5NeverORs_rlE18startSynchronously4name8priority_ScTyxABGSSSg_ScPSgxyYaKcntFZ
 
 // isIsolatingCurrentContext
 Added: _swift_task_invokeSwiftIsIsolatingCurrentContext

test/abi/macOS/x86_64/concurrency.swift

@@ -391,8 +391,8 @@ Added: _swift_task_getCurrentTaskName
 
 // startSynchronously, immediate, addImmediateTask{UnlessCancelled}
 Added: _swift_task_immediate
-Added: _$sScTss5Error_pRs_rlE18startSynchronously4name8priority_ScTyxsAA_pGSSSg_ScPSgxyYaKYAcntFZ
-Added: _$sScTss5NeverORs_rlE18startSynchronously4name8priority_ScTyxABGSSSg_ScPSgxyYaKYAcntFZ
+Added: _$sScTss5Error_pRs_rlE18startSynchronously4name8priority_ScTyxsAA_pGSSSg_ScPSgxyYaKcntFZ
+Added: _$sScTss5NeverORs_rlE18startSynchronously4name8priority_ScTyxABGSSSg_ScPSgxyYaKcntFZ
 
 // isIsolatingCurrentContext
 Added: _swift_task_invokeSwiftIsIsolatingCurrentContext