Block bad words for package names

[ken-matsui]

Can we somehow block bad words for package names? We need this feature in the server as well and this can be implemented here:

poac/src/Manifest.cc

Lines 202 to 242 in 6e5cdda

	// Returns an error message if the package name is invalid.
	std::optional<std::string> // TODO: result-like types make more sense.
	validatePackageName(const std::string_view name) noexcept {
	// Empty
	if (name.empty()) {
	return "must not be empty";
	}
	// Only one character
	if (name.size() == 1) {
	return "must be more than one character";
	}
	// Only lowercase letters, numbers, dashes, and underscores
	for (const char c : name) {
	if (!std::islower(c) && !std::isdigit(c) && c != '-' && c != '_') {
	return "must only contain lowercase letters, numbers, dashes, and "
	"underscores";
	}
	}
	// Start with a letter
	if (!std::isalpha(name[0])) {
	return "must start with a letter";
	}
	// End with a letter or digit
	if (!std::isalnum(name[name.size() - 1])) {
	return "must end with a letter or digit";
	}
	// Using C++ keywords
	const std::unordered_set<std::string_view> keywords = {
	#include "Keywords.def"
	};
	if (keywords.contains(name)) {
	return "must not be a C++ keyword";
	}
	return std::nullopt;
	}