Change the DateFormatSymbols serialized form

Adding locale to the serialized form of
DateFormatSymbols.

Some duplicated code around the generation of
numeric / offset timezone strings (e.g. GMT+08:00) has
been removed. A new hidden method has been added
to TimeZone to create this string.

The timezone string lookup has been moved into
LocaleData and it now has a single path rather
than treating the customZoneStrings path as special.

customZoneStrings has been removed from
DateFormatSymbols because it would potentially
have an incorrect value after serialization and
it is no longer required.

Bug: 16502916
Change-Id: I2b317e34ba4772beb372a75dd08c95113408b9cc
5 files changed