This was a broken test that got all the way to viewer release and the main
branch.

(cherry picked from commit a33a9d29380e6c1a0a9cc539be309d47adef4acf)

Remove all references to LLQueuedThread (but emulate a couple bits of its API
such as handle_t and getPending()).

Migrate ImageRequest into llimageworker.cpp. It has never been part of
LLImageDecodeThread's public API. Remove ImageRequest tests.

Remove all references to LLImageDecodeThread::pause(). The idea of pausing
another thread is bizarre to me, and LLThreadPool has no such operation. Nor
does it have an abortRequest().

SL-16148 SL-16244 SL-16270 SL-16253 Remove most BlockTimers, remove LLMemTracked, introduce alignas, hook most/all reamining allocs, disable synchronous occlusion, and convert frequently accessed LLSingletons to LLSimpleton

stat definition as they don't work on gcc/clang

also, removed LLTrace::init and cleanup
removed derived class implementation of memory stat for LLMemTrackable
is automatic now

copied over scene load frame differencing changes from viewer-interesting
made periodicrecording flexible enough to allow for indefinite number of periods
added scene loading stats floater
fixed collapsing behavior of container views

fix for unit test failures...cleanup apr without destroying
pools, allowing LLProxy to clean itself up as a singleton (and
avoiding spurious dependencies associated with manually destorying
singletons that rely on apr pools)

created separate constructor for static allocation of sampler buffer
fixed start/stop/resume semantics of samplers and added sampler time interval tracking

fixed various issues related to unit tests and LLThreadLocalPtr initialization and teardown

follow up to fix test compiles.