Allow reading for mixed atomic semantics.
Allow reading for mixed atomic semantics.

This relaxes constraints on mixed atomic / lock protected fields. We
explicitly allow reads in this case, since this should be safe.

PiperOrigin-RevId: 414476414

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor