We hypothesized that tests take longer and fail more often when the US is
online. We didn't find strong evidence for this claim. There could be a slight
correlation between the US being online and the tests failing more often.
Even with a weak correlation, there isn't much we can do except improve the
test suite. Therefore, keeping the tests running on a schedule doesn't make
sense.

Finishing multiple spans on different threads that cancel and
reschedule the idle timeout for user interaction transactions
could lead to EXC_BAD_ACCESS crashes. This is fixed now by
synchronizing the access to the idleTimeout block.

Fixes GH-3002

In #3018, there was a change to add locking where `processBacktrace` mutated data structures that could be accessed concurrently. It attempted to separate the code that did not access the shared data structures, and moved all mutating code to a section at the end of the function. However, it missed a few reads from those data structures that also needed to be synchronized (e.g. `frames.count` and `stacks.count`). Generally, separating the critical section from the rest of the logic in that function is not worth the pain because the taking the lock for the entire duration of the function is not expensive.

This refactor adds a new type, `SentryProfilingState`, that centralizes all logic for reading/writing the shared data structures. This has the additional benefit that you no longer need a `processBacktrace` function that takes many parameters where the lifetime of those parameters is unclear (this will be helpful for fixing the memory leaks in a subsequent PR).

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Co-authored-by: Sentry Github Bot <bot+github-bot@sentry.io>