Encodes a string with MQTT length prefix.
MQTT strings are prefixed with a 2-byte big-endian length. Maximum string length is 65,535 bytes.
The string to encode
The length-prefixed UTF-8 bytes
RangeError if the encoded string exceeds 65,535 bytes
MQTT 5.0 ยง1.5.4
Encodes a string with MQTT length prefix.
MQTT strings are prefixed with a 2-byte big-endian length. Maximum string length is 65,535 bytes.