Improve trip display name

[Altonss]

Related to public-transport/transitous#886

[Altonss]

Also I don't really understand this block just before, for me this isn't need as just the logic route short name > route long should be used.

nigiri/src/loader/gtfs/trip.cc

Lines 230 to 244 in 98c239b

	// route name looks like product name, trip name is number
	auto const is_product_name = [=](std::string_view route) {
	return utl::all_of(route, [=](char const c) { return !is_digit(c); });
	};
	auto const is_trip_number = [=](std::string_view trip_name) {
	return utl::all_of(trip_name, is_digit);
	};
	if (!route_->short_name_.empty() && is_product_name(route_->short_name_) &&
	!short_name_.empty() && is_trip_number(short_name_)) {
	return fmt::format("{} {}", route_->short_name_,
	utl::parse<int>(short_name_));
	}

[jbruechert]

This doesn't work for all feeds that use semantic naming instead of the google maps convention.
That is as far as I know most of the data for Germany and Austria

[Altonss]

What exactly doesn't work, not prefering trip short name?
Do you have any specific example in mind?

[Altonss]

This should improve the trip short name in the UK, and also for RER in Paris (France).