AAPT2: whitelist alphanums instead of blacklisting hyphens in package names.

BCP 47 uses plus signs for name mangling, and future qualifiers may
start using other reserved characters as well, so we might as well
futureproof the sanitizer.

Change-Id: I1be7ee4234f8e30bb0ea832372b4dc932d30550c
Fixes: 69134786
Test: UtilTest.SplitNamesAreSanitized