Move raw_string_ostream back to raw_ostream.cpp (#79224)

The implementation of raw_string_ostream::write_impl() was moved to
raw_socket_stream.cpp when the raw_socket_ostream support was separated.
This patch moves it back to facilitate disabling socket support in
downstream projects.

Author: Andy Kaylor

llvm/lib/Support/raw_ostream.cpp

@@ -954,6 +954,14 @@ bool raw_fd_stream::classof(const raw_ostream *OS) {
   return OS->get_kind() == OStreamKind::OK_FDStream;
 }
 
+//===----------------------------------------------------------------------===//
+//  raw_string_ostream
+//===----------------------------------------------------------------------===//
+
+void raw_string_ostream::write_impl(const char *Ptr, size_t Size) {
+  OS.append(Ptr, Size);
+}
+
 //===----------------------------------------------------------------------===//
 //  raw_svector_ostream
 //===----------------------------------------------------------------------===//

llvm/lib/Support/raw_socket_stream.cpp

@@ -170,10 +170,3 @@ raw_socket_stream::createConnectedUnix(StringRef SocketPath) {
 
 raw_socket_stream::~raw_socket_stream() {}
 
-//===----------------------------------------------------------------------===//
-//  raw_string_ostream
-//===----------------------------------------------------------------------===//
-
-void raw_string_ostream::write_impl(const char *Ptr, size_t Size) {
-  OS.append(Ptr, Size);
-}