Optimize UTF8 string/byte conversions

String/byte conversions may take either a Charset instance or its canonical name. One might think a Charset instance would be faster due to avoiding a lookup and instantiation of a Charset, but it's not. The canonical string name variants will cache the string encoder/decoder (obtained from a Charset) resulting in better performance.

LOG4J2-935 describes a real-world performance boost. I micro-benched a marginal runtime improvement on jdk 7/8. However for a 16 byte path, using the canonical name generated 50% less garbage. For a 64 byte path, 25% of the garbage. Given the sheer number of times that paths are (re)parsed, the cost adds up quickly.