Make reduce(inout:) take its initial value owned

Author: airspeedswift

stdlib/public/core/SequenceAlgorithms.swift

@@ -723,7 +723,7 @@ extension Sequence {
   /// - Complexity: O(*n*), where *n* is the length of the sequence.
   @inlinable
   public func reduce<Result>(
-    into initialResult: Result,
+    into initialResult: __owned Result,
     _ updateAccumulatingResult:
       (_ partialResult: inout Result, Element) throws -> ()
   ) rethrows -> Result {

test/api-digester/Outputs/stability-stdlib-abi.swift.expected

@@ -528,3 +528,5 @@ Class _StringStorage has changed its super class from _AbstractStringStorage to
 Constructor _AbstractStringStorage.init() has been removed
 Func _AbstractStringStorage.copy(with:) has been removed
 Func _AbstractStringStorage.getOrComputeBreadcrumbs() has been removed
+
+Func Sequence.reduce(into:_:) has parameter 0 changing from Default to Owned

test/api-digester/Outputs/stability-stdlib-source.swift.expected

@@ -210,3 +210,5 @@ Func LazyCollectionProtocol.map(_:) has been removed
 Func LazyCollectionProtocol.prefix(while:) has been removed
 Func LazyCollectionProtocol.reversed() has been removed
 Var LazyCollectionProtocol.lazy has declared type change from LazyCollection<Self.Elements> to LazySequence<Self.Elements>
+
+Func Sequence.reduce(into:_:) has parameter 0 changing from Default to Owned