Revert "Revert "Consolidate byte to/from hex methods to use HexEncoding.""

Returns to the original submission, plus a fix to CurrencyTest and a bunch
of exception serialization tests that were missed in the first batch.

This reverts commit e52f28fd.
Bug: 63153182
Test: cts -m CtsLibcoreTestCases

Change-Id: Iebcfddef2e9a2775bb7e489955998437f0999e02