Avoid creating unnecessary builder objects in BidiFormatter.

Previously, BidiFormatter.getInstance() created an unnecessary
pass-through builder object, which was used to return a static
already existing BidiFormatter.

Now, we just return the same static BidiFormatter, without going
through a builder, so we can save some extra allocations.

Bug: 10022222

Change-Id: Ibcb6aac1c1e16d9ec00e93824fa063f8dccdf8cb