ART: Relayout BaseMutex and Mutex

Reduce size of BaseMutex (and thus all derived mutex classes) by changing
the field layout. Reduction from 24B to 16B on 64-bit systems.

Bug: 79365543
Test: m test-art-host
Change-Id: Id7b50aa9af1ae5d249e62573ab67257c12922bfa
2 files changed