refactor(i18n): remove std::vector from public API

Reduce our use of std::vector in non-test code to reduce binary bloat:
#689

src/quick-lint-js/i18n/locale.cpp

@@ -93,14 +93,12 @@ std::optional<int> find_locale(const char* locales, const char* locale_name) {
   return found_entry;
 }
 
-std::vector<std::string> locale_name_combinations(const char* locale_name) {
-  std::vector<std::string> locale_names;
-  locale_name_combinations(locale_name,
-                           [&](std::string_view current_locale) -> bool {
-                             locale_names.emplace_back(current_locale);
-                             return true;
-                           });
-  return locale_names;
+void enumerate_locale_name_combinations(
+    const char* locale_name,
+    Temporary_Function_Ref<bool(std::string_view locale)> callback) {
+  return locale_name_combinations<
+      Temporary_Function_Ref<bool(std::string_view locale)>>(
+      locale_name, std::move(callback));
 }
 
 namespace {

src/quick-lint-js/i18n/locale.h

@@ -5,8 +5,8 @@
 
 #include <cstring>
 #include <optional>
-#include <string>
-#include <vector>
+#include <quick-lint-js/port/function-ref.h>
+#include <string_view>
 
 namespace quick_lint_js {
 // Returns the index of the matching locale.
@@ -15,7 +15,10 @@ namespace quick_lint_js {
 // result will be 1.
 std::optional<int> find_locale(const char* locales, const char* locale_name);
 
-std::vector<std::string> locale_name_combinations(const char* locale_name);
+// For testing only.
+void enumerate_locale_name_combinations(
+    const char* locale_name,
+    Temporary_Function_Ref<bool(std::string_view locale)>);
 }
 
 // quick-lint-js finds bugs in JavaScript programs.

test/test-locale.cpp

@@ -11,6 +11,16 @@ using namespace std::literals::string_view_literals;
 
 namespace quick_lint_js {
 namespace {
+std::vector<std::string> locale_name_combinations(const char* locale_name) {
+  std::vector<std::string> locale_names;
+  enumerate_locale_name_combinations(
+      locale_name, [&](std::string_view current_locale) -> bool {
+        locale_names.emplace_back(current_locale);
+        return true;
+      });
+  return locale_names;
+}
+
 TEST(Test_Locale, combinations_for_language) {
   EXPECT_THAT(locale_name_combinations("en"), ElementsAreArray({"en"}));
 }