Cache all Charset instances with their aliases

Replaced type-less Object[] Charset.cache1 field type with more sane
Map.Entry. Charset.cache2 is now a HashMap that keeps all created
Charsets keyed by all of their names (canonical+aliases).

Bug: 26140874
Change-Id: I5f23a28e6c581ae0b5e973fe7cc24600e9dc9c27
1 file changed