Simplify our DecimalFormat.

Simplify our DecimalFormat.

Both the is-a and has-a hierarchies for our DecimalFormat implementation were
over-complicated. This patch starts to address that, and makes cloning twice
as fast (50us versus 100us), but not as fast as I'd like (<10us), and without
making much of a dent in the time it takes to create a new NumberFormat (550us
versus 600us).

The speed of cloning is important because Formatter has a hack that uses it,
and I want to change NumberFormat so that it always hands out clones... at
least until I have time to make "new NumberFormat" acceptably fast.

Also fixes DecimalFormat.applyLocalizedPattern (which used to behave as if
you'd called applyPattern).