Optimize StringBuffer/Builder#appendFloat/Double/Boolean

Moved FloatingDecimal from sun.misc to java.lang package,
so it can access AbstractStringBuilder class (and do
not duplicate same code for the StringBuffer and the
StringBuilder).

FloatingDecimal is no longer instantiated, but
accessed from thread local storage and reused.

Change-Id: Id1c45cfe6f6a8b30b8550fc04ed1976772f28905
6 files changed