Performance: use the JDK UTF-8 encoder for long strings in Writer.writeString / writeStringEscaped, and stop escaping double quotes

Writer.writeString and Writer.writeStringEscaped encode UTF-8 strings directly into socket buffer.

Since Java 17 compact strings, it's now faster to use getBytes(UTF_8), even if that's create a new buffer, this is now faster that using directly the socket buffer for string bigger than 32 bytes.