Split statement-specific parts of semantics_handle.cpp into separate files. (#2949)

`semantics_handle.cpp` is a little on the large side, and is going to grow as we add new nodes. Some of the statement-specific parts have already been split into their own files. Split out the remaining such parts.

toolchain/semantics/semantics_handle_loop_statement.cpp

@@ -0,0 +1,65 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include "toolchain/semantics/semantics_context.h"
+#include "toolchain/semantics/semantics_node.h"
+
+namespace Carbon {
+
+auto SemanticsHandleBreakStatement(SemanticsContext& context,
+                                   ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleBreakStatement");
+}
+
+auto SemanticsHandleBreakStatementStart(SemanticsContext& context,
+                                        ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleBreakStatementStart");
+}
+
+auto SemanticsHandleContinueStatement(SemanticsContext& context,
+                                      ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleContinueStatement");
+}
+
+auto SemanticsHandleContinueStatementStart(SemanticsContext& context,
+                                           ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleContinueStatementStart");
+}
+
+auto SemanticsHandleForHeader(SemanticsContext& context,
+                              ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleForHeader");
+}
+
+auto SemanticsHandleForHeaderStart(SemanticsContext& context,
+                                   ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleForHeaderStart");
+}
+
+auto SemanticsHandleForIn(SemanticsContext& context, ParseTree::Node parse_node)
+    -> bool {
+  return context.TODO(parse_node, "HandleForIn");
+}
+
+auto SemanticsHandleForStatement(SemanticsContext& context,
+                                 ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleForStatement");
+}
+
+auto SemanticsHandleWhileCondition(SemanticsContext& context,
+                                   ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleWhileCondition");
+}
+
+auto SemanticsHandleWhileConditionStart(SemanticsContext& context,
+                                        ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleWhileConditionStart");
+}
+
+auto SemanticsHandleWhileStatement(SemanticsContext& context,
+                                   ParseTree::Node parse_node) -> bool {
+  return context.TODO(parse_node, "HandleWhileStatement");
+}
+
+}  // namespace Carbon