[Lua] Unicode code point to UTF-8 sequence

cp2seq.lua

---@param code integer
function cp2seq(code)
	if code <= 0x7F then
		-- 0xxxxxxx
		return string.char(code)
	elseif code <= 0x7FF then
		-- 110xxxxx 10xxxxxx
		return string.char(
			0xC0 + math.floor(code / 0x40),
			0x80 + code % 0x40)
	elseif code <= 0xFFFF then
		-- 1110xxxx 10xxxxxx 10xxxxxx
		return string.char(
			0xE0 + math.floor(code / 0x1000),
			0x80 + math.floor(code / 0x40) % 0x40,
			0x80 + code % 0x40
		)
	elseif code <= 0x1FFFFF then
		-- 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
		return string.char(
			0xF0 + math.floor(code / 0x40000),
			0x80 + math.floor(code / 0x1000) % 0x40,
			0x80 + math.floor(code / 0x40) % 0x40,
			0x80 + code % 0x40
		)
	else
		return ""
	end
end