For-range in replacement logic (#631)

This replaces GetAstMatcher with AddMatcher because cxxForRangeStmt is a StatementMatcher. addMatcher has multiple definitions (https://clang.llvm.org/doxygen/classclang_1_1ast__matchers_1_1MatchFinder.html) and so this approach allows using the right addMatcher without writing per-call overloads.

To handle the `var`, I'm considering something like moving VarDecl logic into a VarMatcherBase so that I can just use CXXForRangeStmt's getLoopVariable. The problem is a for-range statement has multiple VarDecls, and getLoopVariable may be the easiest way to identify the real one.

migrate_cpp/cpp_refactoring/for_range_test.cpp

@@ -0,0 +1,52 @@
+// 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 "migrate_cpp/cpp_refactoring/for_range.h"
+
+#include "migrate_cpp/cpp_refactoring/matcher_test_base.h"
+
+namespace Carbon {
+namespace {
+
+class ForRangeTest : public MatcherTestBase<ForRangeFactory> {};
+
+TEST_F(ForRangeTest, Basic) {
+  constexpr char Before[] = R"cpp(
+    void Foo() {
+      int items[] = {1};
+      for (int i : items) {
+      }
+    }
+  )cpp";
+  constexpr char After[] = R"(
+    void Foo() {
+      int items[] = {1};
+      for (int i  in  items) {
+      }
+    }
+  )";
+  ExpectReplacement(Before, After);
+}
+
+TEST_F(ForRangeTest, NoSpace) {
+  // Do not mark `cpp` so that clang-format won't "fix" the `:` spacing.
+  constexpr char Before[] = R"(
+    void Foo() {
+      int items[] = {1};
+      for (int i:items) {
+      }
+    }
+  )";
+  constexpr char After[] = R"(
+    void Foo() {
+      int items[] = {1};
+      for (int i in items) {
+      }
+    }
+  )";
+  ExpectReplacement(Before, After);
+}
+
+}  // namespace
+}  // namespace Carbon