message: Tweak `install` input parsing to match `remove`
diff: @@ -238,12 +238,12 @@ namespace vcpkg::Commands::Install
  static const std::string example = Commands::Help::create_example_string("install zlib zlib:x64-windows curl boost");
  args.check_min_arg_count(1, example);
  - auto specs = Util::fmap(args.command_arguments, [&](auto&& arg)
  + const std::vector<PackageSpec> specs = Util::fmap(args.command_arguments, [&](auto&& arg)
  {
  - auto spec = Input::check_and_get_package_spec(arg, default_target_triplet, example);
  - Input::check_triplet(spec.target_triplet(), paths);
  - return spec;
  + return Input::check_and_get_package_spec(arg, default_target_triplet, example);
  });
  + for (auto&& spec : specs)
  + Input::check_triplet(spec.target_triplet(), paths);
  const std::unordered_set<std::string> options = args.check_and_get_optional_command_arguments({ OPTION_DRY_RUN });
  const bool dryRun = options.find(OPTION_DRY_RUN) != options.cend();
  