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/BUILD

@@ -11,6 +11,7 @@ cc_binary(
     srcs = ["main.cpp"],
     deps = [
         ":fn_inserter",
+        ":for_range",
         ":var_decl",
         "@llvm-project//clang:tooling",
     ],
@@ -62,6 +63,24 @@ cc_test(
     ],
 )
 
+cc_library(
+    name = "for_range",
+    srcs = ["for_range.cpp"],
+    hdrs = ["for_range.h"],
+    deps = [":matcher"],
+)
+
+cc_test(
+    name = "for_range_test",
+    srcs = ["for_range_test.cpp"],
+    deps = [
+        ":for_range",
+        ":matcher_test_base",
+        "@llvm-project//clang:tooling",
+        "@llvm-project//llvm:gtest_main",
+    ],
+)
+
 cc_library(
     name = "var_decl",
     srcs = ["var_decl.cpp"],