Revert "Exposed StringBuilder to the outside world which gets us a bit more performance."

This reverts commit 0b4472cedf560f538b0c9f4b08db15ab094dd2fd.
Reimplemented the optimisations removed when unexposing StringBuilder.
Removing use of the pipe operator.
Optimised how Strings were appended and cut the time in half for the example case used in the benchmark.