Add service for dumping at NORMAL priority

SystemUIService is hard-coded to dump at CRITICAL priority and so can't
dump very much (and, most importantly, can't handle dumping our length
log buffers). So instead we create a new service,
SystemUIAuxiliaryDumpService, which will dump alongside all other
services in the NORMAL section. Its dump method calls straight into the
DumpManager.

Test: atest, manual
Change-Id: If76f206081a1663e23fc14076b50bef7396e517f