Prevent deadlock in db_stress with DbStressCompactionFilter (#8956)

Prevent deadlock in db_stress with DbStressCompactionFilter (#8956)

Summary:
The cyclic dependency was:

- `StressTest::OperateDb()` locks the mutex for key 'k'
- `StressTest::OperateDb()` calls a function like `PauseBackgroundWork()`, which waits for pending compaction to complete.
- The pending compaction reaches key `k` and `DbStressCompactionFilter::FilterV2()` calls `Lock()` on that key's mutex, which hangs forever.

The cycle can be broken by using a new function, `port::Mutex::TryLock()`, which returns immediately upon failure to acquire a lock. In that case `DbStressCompactionFilter::FilterV2()` can just decide to keep the key.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8956

Reviewed By: riversand963

Differential Revision: D31183718

Pulled By: ajkr

fbshipit-source-id: 329e4a31ce43085af174cf367ef560b5a04399c5
(cherry picked from commit 791bff5b4e1f0f35448eb2cffa2683e01952038b)

Conflicts:
	port/port_posix.cc -- `errnoStr` is not used in the version
			      we're cherry-picking on. Let's stay
			      with `strerror`.