Add missing standard library header inclusions (#5316)

Discovered by clang-tidy.

toolchain/language_server/context.cpp

@@ -5,6 +5,8 @@
 #include "toolchain/language_server/context.h"
 
 #include <memory>
+#include <optional>
+#include <utility>
 
 #include "common/check.h"
 #include "common/raw_string_ostream.h"

toolchain/language_server/handle_document_symbol.cpp

@@ -3,6 +3,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #include <optional>
+#include <string>
+#include <utility>
+#include <vector>
 
 #include "common/check.h"
 #include "toolchain/language_server/handle.h"

toolchain/language_server/handle_initialize.cpp

@@ -2,6 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <utility>
+
 #include "toolchain/language_server/handle.h"
 
 namespace Carbon::LanguageServer {

toolchain/language_server/handle_shutdown.cpp

@@ -2,6 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <cstddef>
+
 #include "toolchain/language_server/handle.h"
 
 namespace Carbon::LanguageServer {

toolchain/language_server/handle_text_document.cpp

@@ -2,6 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <string>
+#include <tuple>
+#include <vector>
+
 #include "toolchain/language_server/handle.h"
 
 namespace Carbon::LanguageServer {

toolchain/language_server/incoming_messages.cpp

@@ -4,6 +4,8 @@
 
 #include "toolchain/language_server/incoming_messages.h"
 
+#include <utility>
+
 #include "common/ostream.h"
 #include "common/raw_string_ostream.h"
 #include "toolchain/language_server/handle.h"

toolchain/language_server/language_server.cpp

@@ -4,6 +4,8 @@
 
 #include "toolchain/language_server/language_server.h"
 
+#include <memory>
+
 #include "clang-tools-extra/clangd/LSPBinder.h"
 #include "clang-tools-extra/clangd/Transport.h"
 #include "clang-tools-extra/clangd/support/Logger.h"