[stdlib] add OutputSpan

Author: glessard

stdlib/public/core/CMakeLists.txt

@@ -158,6 +158,7 @@ split_embedded_sources(
   EMBEDDED Sort.swift
   EMBEDDED Span/MutableRawSpan.swift
   EMBEDDED Span/MutableSpan.swift
+  EMBEDDED Span/OutputSpan.swift
   EMBEDDED Span/RawSpan.swift
   EMBEDDED Span/Span.swift
   EMBEDDED StaticString.swift

stdlib/public/core/GroupInfo.json

@@ -202,6 +202,7 @@
   "Span": [
     "MutableRawSpan.swift",
     "MutableSpan.swift",
+    "OutputSpan.swift",
     "RawSpan.swift",
     "Span.swift"
   ],