Add missing standard library header inclusions (#5316)

Discovered by clang-tidy.

toolchain/parse/context.cpp

@@ -4,6 +4,7 @@
 
 #include "toolchain/parse/context.h"
 
+#include <initializer_list>
 #include <optional>
 
 #include "common/check.h"

toolchain/parse/dump.cpp

@@ -6,6 +6,8 @@
 
 #include "toolchain/parse/dump.h"
 
+#include <string>
+
 #include "common/raw_string_ostream.h"
 #include "toolchain/lex/dump.h"
 

toolchain/parse/extract.cpp

@@ -2,6 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <initializer_list>
+#include <optional>
 #include <tuple>
 #include <typeinfo>
 #include <utility>

toolchain/parse/handle_decl_scope_loop.cpp

@@ -2,6 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <array>
+
 #include "toolchain/lex/token_kind.h"
 #include "toolchain/parse/context.h"
 #include "toolchain/parse/handle.h"

toolchain/parse/handle_paren_condition.cpp

@@ -2,6 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <optional>
+
 #include "toolchain/parse/context.h"
 #include "toolchain/parse/handle.h"
 

toolchain/parse/handle_statement.cpp

@@ -2,6 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#include <optional>
+
 #include "toolchain/parse/context.h"
 #include "toolchain/parse/handle.h"
 

toolchain/parse/precedence.cpp

@@ -4,6 +4,9 @@
 
 #include "toolchain/parse/precedence.h"
 
+#include <initializer_list>
+#include <optional>
+
 #include "common/check.h"
 
 namespace Carbon::Parse {

toolchain/parse/tree_and_subtrees.cpp

@@ -4,6 +4,9 @@
 
 #include "toolchain/parse/tree_and_subtrees.h"
 
+#include <tuple>
+#include <utility>
+
 #include "toolchain/lex/token_index.h"
 
 namespace Carbon::Parse {

toolchain/parse/tree_test.cpp

@@ -8,6 +8,8 @@
 #include <gtest/gtest.h>
 
 #include <forward_list>
+#include <optional>
+#include <string>
 
 #include "common/raw_string_ostream.h"
 #include "toolchain/base/shared_value_stores.h"