`PrettyPrintWriter` cannot write emoji in XML 1.1 mode

[jglick]

See jenkinsci/jenkins#7924; can draft a unit test for this repo in case it is not obvious. In XML_1_1 mode, writeText uses charAt rather than codePointAt and so throws an error when given a supplementary code point character.

[joehni]

This is actual because codePointAt() does not exist in Java 1.4. It is really time for 1.5.x...