[NFC][TSan] Lock ThreadRegistryLock inside ScopedReport::AddThread and AddLocation (#228814)
Among ScopedReport methods, only AddThread and AddLocation
(via IsThreadStackOrTls) have ever accessed ctx->thread_registry;
AddMemoryAccess, AddMutex, AddStack, AddSleep, AddUniqueTid, and
SetCount only populate ScopedReport::rep_.
Now that ScopedReport's constructor (#228614) and ReportRace (#228813)
no longer require callers to hold ThreadRegistryLock, acquire
ThreadRegistryLock inside ScopedReport::AddThread and
ScopedReport::AddLocation instead of locking ctx->thread_registry in
each caller around ScopedReport population.
Assisted-by: Gemini